refactor(brand): rename F∆I -> Ch∆In + hub binary fai -> chain

Studio follows the platform rename: product branding F∆I -> Ch∆In in UI
strings, command examples fai -> chain, and — critically — the spawned
hub binary path ~/.fai/bin/fai -> ~/.fai/bin/chain so Studio launches
the renamed binary. The fai_* Dart identifiers (FaiLog, widget files,
the generated SDK) stay = vendor/internal namespace. flutter analyze:
no issues.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/l10n/app_en.arb

@@ -1,11 +1,11 @@
 {
   "@@locale": "en",
-  "appTitle": "F∆I Studio",
+  "appTitle": "Ch∆In Studio",
   "@appTitle": {
     "description": "App-bar title in the OS task switcher."
   },
   "navWelcome": "Welcome",
-  "welcomeHeroTitle": "F∆I Platform",
+  "welcomeHeroTitle": "Ch∆In Platform",
   "welcomeHeroSubtitle": "Deterministic workflow engine for AI-assisted document processing in regulated environments.",
   "welcomePillarHubTitle": "Hub",
   "welcomePillarHubBody": "One Rust binary that loads modules and runs flows. SQLite for state. No Docker, no message broker, no background services to babysit.",
@@ -63,7 +63,7 @@
   "welcomeChecklistMcp": "Add a public capability source",
   "welcomeChecklistMcpHint": "Add an MCP source from the Store, or configure one under Settings → MCP Clients.",
   "welcomeChecklistModule": "Install a text module",
-  "welcomeChecklistModuleHint": "Install a module from the Store — pick whichever category fits your work. Modules are sandboxed F∆I components.",
+  "welcomeChecklistModuleHint": "Install a module from the Store — pick whichever category fits your work. Modules are sandboxed Ch∆In components.",
   "welcomeChecklistFlow": "Run a saved flow",
   "welcomeChecklistFlowHint": "Flows → pick one → Run. Studio ships a few demo flows; one of your own works too.",
   "welcomeChecklistAllDone": "All four steps complete.",
@@ -323,7 +323,7 @@
   },
   "storeReloadTooltip": "Reload",
   "storeTodayBadge": "TODAY",
-  "storeTodayDeck": "From the F∆I editor",
+  "storeTodayDeck": "From the Ch∆In editor",
   "storeTodayDismissTooltip": "Hide for this session",
   "storePillInstalled": "installed",
   "storePillUpdate": "update",
@@ -610,7 +610,7 @@
   "auditClearLogButton": "Clear log",
   "modulesTitle": "Modules",
   "modulesNoneTitle": "No modules yet",
-  "modulesNoneHint": "Run `fai install <capability-name>` or check ~/.fai/modules/.",
+  "modulesNoneHint": "Run `chain install <capability-name>` or check ~/.fai/modules/.",
   "modulesReloadTooltip": "Reload",
   "modulesRecentActivity": "RECENT ACTIVITY",
   "modulesRecentActivityHint": "last {n} install/uninstall events from the audit log",
@@ -670,7 +670,7 @@
   "flowsTitle": "Flows",
   "flowsReloadTooltip": "Reload",
   "flowsNoneTitle": "No saved flows",
-  "flowsNoneHint": "Save a flow with `fai admin flows save <name> <flow.yaml>` and it shows up here.",
+  "flowsNoneHint": "Save a flow with `chain admin flows save <name> <flow.yaml>` and it shows up here.",
   "flowsRunDialogTitle": "Run {name}",
   "@flowsRunDialogTitle": {
     "placeholders": {
@@ -852,7 +852,7 @@
   "welcomeChecklistNextTodayBody": "Run tools/today/propose.sh on a cron and the editorial card on the store auto-fills with operator-curated narratives.",
   "welcomeChecklistNextTodayButton": "Open Today docs",
   "welcomeChecklistNextModuleTitle": "Build your own module",
-  "welcomeChecklistNextModuleBody": "Generate a Rust+WASM scaffold with `fai new module <name>`. The module-sdk handles the WIT plumbing; you write a typed invoke.",
+  "welcomeChecklistNextModuleBody": "Generate a Rust+WASM scaffold with `chain new module <name>`. The module-sdk handles the WIT plumbing; you write a typed invoke.",
   "welcomeChecklistNextModuleButton": "Read the docs",
   "auditGroupToday": "TODAY",
   "auditGroupYesterday": "YESTERDAY",
@@ -957,7 +957,7 @@
   "errInternal": "Unexpected internal error.",
   "errInternalHint": "Check the hub logs at `~/.fai/logs/`. If this repeats, please report it.",
   "errUnavailable": "Hub not reachable.",
-  "errUnavailableHint": "Make sure `fai serve` (or `fai daemon start`) is running and the daemon endpoint matches Studio's settings.",
+  "errUnavailableHint": "Make sure `chain serve` (or `chain daemon start`) is running and the daemon endpoint matches Studio's settings.",
   "errUnauthenticated": "Authentication required.",
   "errUnauthenticatedHint": "Set `FAI_REGISTRY_TOKEN` or sign in through Settings before retrying.",
   "errCopyDetail": "Copy detail",
@@ -1176,7 +1176,7 @@
   "doctorStatusUnknown": "Daemon status: …",
   "doctorPillRunning": "running",
   "doctorPillStopped": "stopped",
-  "doctorDaemonControlHint": "Studio shells out to the platform binary — mirrors `fai daemon …` exactly so the CLI and UI stay in lockstep.",
+  "doctorDaemonControlHint": "Studio shells out to the platform binary — mirrors `chain daemon …` exactly so the CLI and UI stay in lockstep.",
   "doctorDaemonControlWorking": "Working…",
   "doctorPathLog": "Log",
   "doctorPathConfig": "Config",
@@ -1184,7 +1184,7 @@
   "doctorPathModules": "Modules dir",
   "doctorPathFlows": "Flows dir",
   "doctorPathPid": "PID file",
-  "doctorPathsEmpty": "Daemon did not report file paths. Update the running hub via `fai daemon restart`.",
+  "doctorPathsEmpty": "Daemon did not report file paths. Update the running hub via `chain daemon restart`.",
   "doctorOpenError": "Could not open: {detail}",
   "@doctorOpenError": {
     "placeholders": {
@@ -1201,7 +1201,7 @@
       }
     }
   },
-  "doctorUpdateBody": "Channel {channel} now offers {version}. Apply via the button — Studio shells out to `fai update apply --channel {channel}`.",
+  "doctorUpdateBody": "Channel {channel} now offers {version}. Apply via the button — Studio shells out to `chain update apply --channel {channel}`.",
   "@doctorUpdateBody": {
     "placeholders": {
       "channel": {
@@ -1241,7 +1241,7 @@
   "n8nHint": "Active n8n workflows surface as `n8n.<endpoint>.<slug>` capabilities. Configure once, see them in the Store.",
   "n8nEmpty": "No n8n endpoints configured. Click + to add one.",
   "hubUnreachable": "Hub unreachable",
-  "hubUnreachableHint": "Start the hub with `fai serve`.",
+  "hubUnreachableHint": "Start the hub with `chain serve`.",
   "languageEnglish": "English",
   "languageGerman": "Deutsch",
   "searchHint": "Jump anywhere — modules, store, flows, pages…",
@@ -1514,8 +1514,8 @@
   "addSourceField": "URL or path to .fai bundle",
   "addSourceHint": "https://git.flemming.ai/your-org/your-module/releases/download/v0.1.0/foo-0.1.0.fai",
   "addSourceHowItWorksTitle": "How private modules work",
-  "addSourceHowItWorksBody": "A module is a directory with a module.yaml + the WASM artifact. To share it: pack it (`fai pack <dir>`) and host the resulting `.fai` bundle anywhere (your own Forgejo / GitHub / S3). The hub installs by URL and verifies the signature against its trust store.\n\nDeveloping locally? Use the CLI — Studio cannot install from an unpacked directory (yet):",
-  "addSourceCliExample": "fai install --link /path/to/module",
+  "addSourceHowItWorksBody": "A module is a directory with a module.yaml + the WASM artifact. To share it: pack it (`chain pack <dir>`) and host the resulting `.fai` bundle anywhere (your own Forgejo / GitHub / S3). The hub installs by URL and verifies the signature against its trust store.\n\nDeveloping locally? Use the CLI — Studio cannot install from an unpacked directory (yet):",
+  "addSourceCliExample": "chain install --link /path/to/module",
   "addSourceInstallButton": "Install",
   "addSourceCancel": "Cancel",
   "installFailed": "Install failed: {error}",
@@ -1543,7 +1543,7 @@
     }
   },
   "faiBinaryNotFound": "Could not find the `fai` program on this machine.",
-  "faiBinaryNotFoundHint": "Install the F∆I platform, or point Studio at an existing `fai` binary.",
+  "faiBinaryNotFoundHint": "Install the Ch∆In platform, or point Studio at an existing `fai` binary.",
   "faiBinaryLocateButton": "Locate `fai` binary…",
   "faiBinaryInstallDocsButton": "Open install guide",
   "faiBinaryPickerTitle": "Select the `fai` binary",