feat: guided-setup wizard — localized explained options + plain-language plan

Reworks the Setup-Assistent toward the zero-learning-curve bar
(docs/architecture/guided-setup.md, phase 1.1):

- Every scenario/intent/target choice is now a localized option CARD
  with a one-line plain-language explanation of what it configures
  (DE+EN, Sie-form) — replacing the bare dropdowns whose labels were
  English enum humanizations ('Regulated Production', 'This Laptop').
- Three explained steps with a 'Schritt n von 3' progress line
  (stakes → task → environment); the two adaptive toggles move to the
  last step in plain language (no 'air-gapped' jargon).
- The review step renders a localized PLAIN-LANGUAGE summary built
  from 'chain init --answers --plan-json' (the structured SetupPlan) —
  'Ch∆In richtet einen regulierten Betrieb ein: signierte Module
  verlangt · … · geändert wird nur ~/.chain/config.yaml' — instead of
  echoing the CLI's English prose. Warns when an existing config will
  be overwritten. After apply: a plain 'Fertig' + next steps.

flutter analyze clean; widget tests for the step flow + German option
labels. Remaining per plan: clickable follow-up actions, signature
dead-end fix, placement/auto-open, and the LLM free-text path.

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

lib/l10n/app_en.arb

@@ -1734,5 +1734,59 @@
   "workspaceSealedSwitchFailed": "Could not switch to the sealed area: {error}",
   "@workspaceSealedSwitchFailed": {"placeholders": {"error": {"type": "String"}}},
   "sealedIdentityBar": "Sealed area — isolated hub, own data and audit chain",
-  "sealedLeave": "Leave"
+  "sealedLeave": "Leave",
+  "setupStepOf": "Step {n} of {total}",
+  "@setupStepOf": {"placeholders": {"n": {"type": "int"}, "total": {"type": "int"}}},
+  "setupStep1Title": "What are the stakes?",
+  "setupStep2Title": "What do you want to do first?",
+  "setupStep3Title": "Where will it run?",
+  "setupReviewTitle": "This is what Ch∆In will set up",
+  "setupChooseFreeText": "Or just describe what you want to do",
+  "setupScenTryingOut": "Just trying it out",
+  "setupScenTryingOutSub": "A relaxed workspace on this machine — no signing, no audit locking.",
+  "setupScenTeamHub": "A shared team hub",
+  "setupScenTeamHubSub": "A secured hub for several people — signed modules, resource limits.",
+  "setupScenRegulated": "Regulated production",
+  "setupScenRegulatedSub": "Signed modules, a complete tamper-evident audit trail, and a human approval before every AI step.",
+  "setupScenBuildModules": "Building modules",
+  "setupScenBuildModulesSub": "A developer setup for writing and testing your own modules.",
+  "setupIntentHello": "Run the hello example",
+  "setupIntentHelloSub": "Just see one flow run end to end.",
+  "setupIntentExtract": "Extract text from documents",
+  "setupIntentExtractSub": "Pull plain text out of PDF and DOCX files.",
+  "setupIntentExtractSummarize": "Extract and summarize",
+  "setupIntentExtractSummarizeSub": "Extract text, then summarize it.",
+  "setupIntentClassify": "Sort incoming documents",
+  "setupIntentClassifySub": "Extract text, then classify it with an AI step.",
+  "setupIntentBuildModule": "Build my own module",
+  "setupIntentBuildModuleSub": "Start from a module scaffold.",
+  "setupTargetLaptop": "This computer",
+  "setupTargetLaptopSub": "Runs locally on the machine you are on now.",
+  "setupTargetHomeServer": "An on-premise server",
+  "setupTargetHomeServerSub": "A server in your own house — starts on boot, runs in the background.",
+  "setupTargetAirgapped": "A fully local server (no internet)",
+  "setupTargetAirgappedSub": "An isolated server with no internet — the strictest, most private posture.",
+  "setupTargetContainer": "A container",
+  "setupTargetContainerSub": "Docker or Podman, with a ready-made compose snippet.",
+  "setupApprovalPlain": "Ask a person for approval before every AI step",
+  "setupDataLocalPlain": "Data must never leave the building (fully local)",
+  "setupPlanIntroDev": "Ch∆In sets up a straightforward workspace.",
+  "setupPlanIntroEnterprise": "Ch∆In sets up a secured operation for a team.",
+  "setupPlanIntroAirgapped": "Ch∆In sets up a fully local, regulated operation.",
+  "setupPlanSignatures": "Only signed modules are allowed.",
+  "setupPlanWorm": "The audit log is additionally sealed tamper-proof (WORM).",
+  "setupPlanApproval": "Before every AI step, the system asks a person for approval.",
+  "setupPlanModules": "These modules are prepared: {modules}.",
+  "@setupPlanModules": {"placeholders": {"modules": {"type": "String"}}},
+  "setupPlanFlow": "An example flow “{flow}” is created.",
+  "@setupPlanFlow": {"placeholders": {"flow": {"type": "String"}}},
+  "setupPlanFileChanged": "Only one file is changed: {path}.",
+  "@setupPlanFileChanged": {"placeholders": {"path": {"type": "String"}}},
+  "setupPlanOverwriteWarn": "An existing configuration will be overwritten.",
+  "setupApplied": "Done — Ch∆In is set up.",
+  "setupNextTitle": "Next steps",
+  "setupNextHubStart": "Start the hub",
+  "setupNextInstall": "Install the modules",
+  "setupNextRunFlow": "Run the example flow",
+  "setupStartCta": "Get started in 3 questions"
 }