refactor: rename internal Fai* design system + fai_ helpers to chain

The Studio design system, widgets and helpers carried a Fai* / fai_
prefix (FaiSpace, FaiColors, FaiTheme, FaiLog, 17 fai_*.dart files, the
faiBinary* l10n keys). Studio is the Ch∆In product, so rename them to
Chain* / chain_ — carefully preserving English fail/failure/failed.
Also fix stale references: the 'fai' binary in l10n strings -> 'chain',
FAI_* env vars (FAI_BIN/DATA_DIR/MODULES_DIR/TODAY/BOOTSTRAP_TOKEN) ->
CHAIN_*, fai_platform -> fai_chain, fai_hub -> chain_hub. Vendor
security-hook tooling (FAI_BANNED_TERMS_FILE) + the .fai bundle ext left.
flutter analyze + test: clean (20 passed).

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

test/integration/README.md

@@ -35,14 +35,14 @@ flutter test test/integration/
 ```
 
 Prereq: a `fai` binary on PATH or at
-`../fai_platform/target/release/fai`. The harness skips with a
+`../fai_chain/target/release/chain`. The harness skips with a
 clear message when neither exists, so this command does not
 fail on a fresh checkout — it just reports skipped tests.
 
 To get the binary:
 
 ```bash
-cd ../fai_platform
+cd ../fai_chain
 cargo build --release --bin fai
 ```
 
@@ -52,11 +52,11 @@ A cold `chain serve` spends its first ~30s building the
 curated-model database and initialising SQLite migrations.
 `HubFixture.start()` waits up to 60s by default; if your local
 hub takes longer the first time, run `chain serve` once by hand
-against any temp `FAI_DATA_DIR` to warm the per-user cargo /
+against any temp `CHAIN_DATA_DIR` to warm the per-user cargo /
 SBOM caches:
 
 ```bash
-FAI_DATA_DIR=/tmp/fai_warmup chain serve --bind 127.0.0.1:0
+CHAIN_DATA_DIR=/tmp/chain_warmup chain serve --bind 127.0.0.1:0
 # wait for "hub started", Ctrl-C
 ```
 
@@ -66,7 +66,7 @@ Subsequent integration-test runs are quick.
 
 `.forgejo/workflows/ci.yml` doesn't run these yet. Adding them
 needs an artifact-passing pattern: the platform build job
-publishes `target/release/fai` as a CI artifact; the studio
+publishes `target/release/chain` as a CI artifact; the studio
 test job consumes it. Pattern is straightforward once we want
 it; it's deferred because we don't yet have enough integration
 tests to justify the CI runtime.

test/integration/capabilities_test.dart

@@ -22,7 +22,7 @@
 //   flutter test test/integration/
 //
 // CI does not yet run these by default — they need a built `fai`
-// binary in PATH or in ../fai_platform/target/release/. Wire that
+// binary in PATH or in ../chain_platform/target/release/. Wire that
 // in via .forgejo/workflows/ci.yml once the platform CI publishes
 // a Linux binary as an artifact for downstream jobs to consume.
 

test/integration/hub_fixture.dart

@@ -72,7 +72,7 @@ class HubFixture {
       if (skipIfBinaryMissing) {
         markTestSkipped(
           'Hub fixture skipped: no `fai` binary found on PATH or in '
-          '../fai_platform/target/release/fai. Build it with '
+          '../chain_platform/target/release/fai. Build it with '
           '`cargo build --release` and re-run.',
         );
         return null;
@@ -86,15 +86,15 @@ class HubFixture {
 
     // Run as a child process. `serve --bind` lets us avoid the
     // default 50051 (and any local daemon the developer happens
-    // to be running). FAI_DATA_DIR keeps the temp footprint
+    // to be running). CHAIN_DATA_DIR keeps the temp footprint
     // contained — no state leaks into ~/.fai.
     final process = await Process.start(
       binary,
       ['serve', '--bind', addr],
       environment: {
         ...Platform.environment,
-        'FAI_DATA_DIR': tempDir.path,
-        'FAI_MODULES_DIR': '${tempDir.path}/modules',
+        'CHAIN_DATA_DIR': tempDir.path,
+        'CHAIN_MODULES_DIR': '${tempDir.path}/modules',
         // Suppress info logs without a CLI flag — the binary
         // respects RUST_LOG for tracing-subscriber.
         'RUST_LOG': 'warn',
@@ -136,7 +136,7 @@ class HubFixture {
     await tempDir.delete(recursive: true);
     throw StateError(
       'Hub did not become healthy within $readyTimeout. '
-      'Check `fai serve` works manually with FAI_DATA_DIR=$tempDir.',
+      'Check `fai serve` works manually with CHAIN_DATA_DIR=$tempDir.',
     );
   }
 
@@ -172,8 +172,8 @@ class HubFixture {
     }
 
     final candidate = Platform.isWindows
-        ? '../fai_platform/target/release/fai.exe'
-        : '../fai_platform/target/release/fai';
+        ? '../chain_platform/target/release/fai.exe'
+        : '../chain_platform/target/release/fai';
     final f = File(candidate);
     if (await f.exists()) {
       return f.absolute.path;

test/integration/plugin_theme_test.dart

@@ -10,9 +10,9 @@
 //   flutter test test/integration/plugin_theme_test.dart
 //
 // Pre-reqs (handled by HubFixture's skip-when-missing path):
-//   - fai binary on PATH or at ../fai_platform/target/release/fai
+//   - fai binary on PATH or at ../chain_platform/target/release/fai
 //   - studio-theme-solarized plugin built to module.wasm in its
-//     fai_plugins dir.
+//     chain_plugins dir.
 
 import 'dart:io';
 
@@ -33,7 +33,7 @@ void main() {
         // add network + bundle-fetch latency that doesn't
         // belong in an in-process round-trip test.
         final pluginSrc = Directory(
-          '../fai_plugins/studio-theme-solarized',
+          '../chain_plugins/studio-theme-solarized',
         );
         if (!await pluginSrc.exists()) {
           markTestSkipped('studio-theme-solarized source not available');