fix(security): RBAC on legacy create endpoints, hashed API keys, hardening

Addresses findings from the security audit:
- H1: add check_project_role to the legacy misc.py create endpoints
  (milestones=mgr, tasks/supports/meetings=dev) that previously required
  only authentication — closing a cross-project write bypass available to
  any logged-in user or agent API key.
- M2: comments are always attributed to the authenticated caller; the
  client-supplied author_id is dropped (no author spoofing).
- M3: API keys are stored as SHA-256 hashes (key_hash) plus a short
  key_prefix for display — never plaintext. Lookup hashes the presented
  key; listings never expose the secret. Includes an idempotent migration
  for existing deployments.
- M5: the OIDC session cookie's Secure flag is env-driven via
  SESSION_COOKIE_SECURE (default True; set false for plain-HTTP dev).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/schemas/schemas.py

@@ -105,7 +105,9 @@ class CommentBase(BaseModel):
 
 class CommentCreate(CommentBase):
     task_id: int
-    author_id: int
+    # author_id is NOT accepted from the client — the comment is always
+    # attributed to the authenticated caller (server-side) to prevent
+    # author spoofing.
 
 
 class CommentUpdate(BaseModel):