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/features/_example/api-contract.yaml

@@ -0,0 +1,136 @@
+openapi: 3.1.0
+info:
+  title: Familienarchiv API — Profile picture upload
+  version: 0.0.1-SNAPSHOT
+  description: >
+    Design-time contract for the avatar feature (.specify/features/_example).
+    Source of truth once shipped 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:
+      type: apiKey
+      in: cookie
+      name: SESSION
+  schemas:
+    ErrorResponse:
+      type: object
+      required: [code, message]
+      properties:
+        code:
+          type: string
+          example: AVATAR_TOO_LARGE
+        message:
+          type: string
+    UserProfileView:
+      type: object
+      required: [id, displayName]
+      properties:
+        id:
+          type: string
+          format: uuid
+        displayName:
+          type: string
+        avatarUrl:
+          type: [string, "null"]
+          description: Authenticated proxy path (/api/users/{id}/avatar) when an avatar exists, else null.
+          example: /api/users/3f1c.../avatar
+security:
+  - cookieAuth: []
+paths:
+  /api/users/me/avatar:
+    post:
+      summary: Upload or replace the current user's avatar
+      operationId: uploadMyAvatar
+      security:
+        - cookieAuth: []
+      requestBody:
+        required: true
+        content:
+          multipart/form-data:
+            schema:
+              type: object
+              required: [file]
+              properties:
+                file:
+                  type: string
+                  format: binary
+                  description: PNG or JPEG, max 2 MB.
+      responses:
+        '200':
+          description: Avatar stored; updated profile returned.
+          content:
+            application/json:
+              schema: { $ref: '#/components/schemas/UserProfileView' }
+        '400':
+          description: Unsupported type (UNSUPPORTED_FILE_TYPE) or too large (AVATAR_TOO_LARGE).
+          content:
+            application/json:
+              schema: { $ref: '#/components/schemas/ErrorResponse' }
+        '401':
+          description: Unauthenticated (UNAUTHORIZED).
+          content:
+            application/json:
+              schema: { $ref: '#/components/schemas/ErrorResponse' }
+    delete:
+      summary: Remove the current user's avatar
+      operationId: deleteMyAvatar
+      security:
+        - cookieAuth: []
+      responses:
+        '200':
+          description: Avatar removed; profile returned with avatarUrl null.
+          content:
+            application/json:
+              schema: { $ref: '#/components/schemas/UserProfileView' }
+        '401':
+          description: Unauthenticated (UNAUTHORIZED).
+          content:
+            application/json:
+              schema: { $ref: '#/components/schemas/ErrorResponse' }
+  /api/users/{id}/avatar:
+    get:
+      summary: Stream a user's avatar image (authenticated proxy)
+      operationId: getUserAvatar
+      security:
+        - cookieAuth: []
+      parameters:
+        - name: id
+          in: path
+          required: true
+          schema: { type: string, format: uuid }
+      responses:
+        '200':
+          description: Image bytes.
+          content:
+            image/png: { schema: { type: string, format: binary } }
+            image/jpeg: { schema: { type: string, format: binary } }
+        '401': { description: Unauthenticated, content: { application/json: { schema: { $ref: '#/components/schemas/ErrorResponse' } } } }
+        '404': { description: User has no avatar, content: { application/json: { schema: { $ref: '#/components/schemas/ErrorResponse' } } } }
+    delete:
+      summary: Remove another user's avatar (admin only)
+      operationId: deleteUserAvatar
+      description: Requires Permission.ADMIN_USER (enforced by @RequirePermission on the controller).
+      security:
+        - cookieAuth: []
+      parameters:
+        - name: id
+          in: path
+          required: true
+          schema: { type: string, format: uuid }
+      responses:
+        '200':
+          description: Avatar removed.
+          content:
+            application/json:
+              schema: { $ref: '#/components/schemas/UserProfileView' }
+        '401': { description: Unauthenticated, content: { application/json: { schema: { $ref: '#/components/schemas/ErrorResponse' } } } }
+        '403':
+          description: Caller lacks ADMIN_USER (FORBIDDEN).
+          content:
+            application/json:
+              schema: { $ref: '#/components/schemas/ErrorResponse' }