feat(sdd): add .specify scaffold — constitution, AGENTS, personas, templates, example, RTM

Introduces the SDD root: a v1.0.0 constitution and machine-readable AGENTS.md
grounded in the project's real conventions; six EARS-aware persona spec-review
checklists that cross-reference .claude/personas/; feature-spec/ADR/threat-model/
api-contract templates; a fully worked _example feature; a living RTM; and an
adrs/ pointer that reuses the existing docs/adr/ archive.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.specify/templates/api-contract-stub.md

@@ -0,0 +1,94 @@
+# API Contract Stub
+
+This project is **REST + OpenAPI**. The backend serves the live spec via springdoc at
+`http://localhost:8080/v3/api-docs` (dev profile only), and the frontend generates its
+TypeScript client from it with `npm run generate:api` (`openapi-typescript` →
+`frontend/src/lib/generated/api.ts`). There is no GraphQL in this stack.
+
+> **The live spec is generated from the Java controllers — it is the source of truth.** A
+> hand-written contract under `.specify/features/<name>/api-contract.yaml` is a *design
+> artifact*: it pins the intended shape during spec review and is checked against the
+> generated spec once the endpoint exists. Keep it OpenAPI **3.1**, and keep
+> `@Schema(requiredMode = REQUIRED)` on the Java side as the real driver of `required`.
+
+## How to use this stub
+
+1. Copy the skeleton below to `.specify/features/<name>/api-contract.yaml`.
+2. Fill in the paths/methods/schemas your feature adds. Every mutating path documents the
+   `403`/`401` responses and the `cookieAuth` security requirement (matching the real
+   `@RequirePermission` gate).
+3. The `sdd-gate.yml` CI job lints any changed `api-contract.yaml` with Spectral
+   (`npx @stoplight/spectral-cli lint`). Run it locally the same way before pushing.
+4. After the endpoint ships, run `npm run generate:api` and diff the generated types against
+   this contract; reconcile any drift (the generated spec wins — update the contract).
+
+## OpenAPI 3.1 skeleton
+
+```yaml
+openapi: 3.1.0
+info:
+  title: Familienarchiv API — <feature name>
+  version: 0.0.1-SNAPSHOT
+  description: Design-time contract for <feature>. Source of truth is the generated /v3/api-docs.
+servers:
+  - url: http://localhost:8080
+    description: Local backend (dev profile)
+  - url: https://archiv.raddatz.cloud
+    description: Production (behind Caddy)
+components:
+  securitySchemes:
+    cookieAuth:               # Spring Session JDBC — opaque session id in the SESSION cookie
+      type: apiKey
+      in: cookie
+      name: SESSION
+  schemas:
+    ErrorResponse:            # shape produced by GlobalExceptionHandler
+      type: object
+      required: [code, message]
+      properties:
+        code:
+          type: string
+          description: Machine-readable ErrorCode (see ErrorCode.java / errors.ts).
+          example: FORBIDDEN
+        message:
+          type: string
+    # <YourResponseView>:     # always a view, never a lazy-collection entity (ADR-036)
+    #   type: object
+    #   required: [id]
+    #   properties:
+    #     id: { type: string, format: uuid }
+security:
+  - cookieAuth: []            # default: every path requires a session unless overridden to []
+paths:
+  /api/<resource>:
+    post:
+      summary: <create …>
+      operationId: <createResource>
+      security:
+        - cookieAuth: []      # plus @RequirePermission(Permission.X) on the controller
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema: { $ref: '#/components/schemas/<CreateDTO>' }
+      responses:
+        '201':
+          description: Created
+          content:
+            application/json:
+              schema: { $ref: '#/components/schemas/<YourResponseView>' }
+        '400': { description: Validation failed, content: { application/json: { schema: { $ref: '#/components/schemas/ErrorResponse' } } } }
+        '401': { description: Unauthenticated, content: { application/json: { schema: { $ref: '#/components/schemas/ErrorResponse' } } } }
+        '403': { description: Missing permission, content: { application/json: { schema: { $ref: '#/components/schemas/ErrorResponse' } } } }
+```
+
+## Validating the contract in CI
+
+The `sdd-gate.yml` workflow runs, on PRs that touch a `api-contract.yaml`:
+
+```bash
+npx @stoplight/spectral-cli lint .specify/features/**/api-contract.yaml
+```
+
+Spectral's default OpenAPI ruleset catches malformed specs, missing `operationId`s, and
+undefined `$ref`s. Add a `.spectral.yaml` at the repo root to tune rules if needed.