fix: P0 hardening — fail-closed SECRET_KEY, locked CORS, role-safe registration (HARDENING.md P0.1/P0.2/P0.3)

P0.1 — fail-closed secrets:
- config.py: no default SECRET_KEY; refuses to boot when unset, a known
  placeholder, or <32 chars. Generate with: openssl rand -hex 32.
- docker-compose.yml: literal secrets removed; runtime env now comes from
  a git-ignored .env via env_file. .env.example added as template.
- .gitignore already covers .env (verified).

P0.2 — locked CORS:
- main.py: CORS_ORIGINS must be an explicit comma-separated allow-list.
  '*' or an empty value refuses to boot (was: silently ['*'] with
  allow_credentials=True).

P0.3 — role-safe registration:
- services/auth.py: client-supplied 'role' is IGNORED on POST
  /api/auth/register; self-registered users always get the
  least-privilege 'CS Rep' role. Unauthenticated callers can no longer
  mint Admin/Jerome, Admin/Wahab, or Director accounts.

Tests:
- conftest.py sets test SECRET_KEY/CORS_ORIGINS before app import.
- New tests/test_p0_hardening.py (8 tests): role-escalation blocked for
  Admin/Jerome and Admin/Wahab, duplicate-email 409, and subprocess
  boot-validation for placeholder/short/missing secret + wildcard CORS.
- Full suite: 44 passed.

Redeploy note (per research): seed_units/seed_categories are insert-only,
so the Aug-26 redeploy does NOT orphan historical tickets referencing
units 103E/103W/105E/105W or the legacy 34-category tree. Pending
Wahab: are 103E/103W/105E/105W real apartments dropped from the Excel
regeneration? Optional follow-up: floor-number backfill for already-
seeded units (mapping corrected floors; existing rows keep old values).

Checks per HARDENING.md acceptance:
- [x] starting without a real key fails loudly (subprocess-verified)
- [x] compose carries no literal secret; secrets come from .env
- [x] CORS_ORIGINS explicit allow-list, '*' rejected
- [x] unauthenticated register cannot mint Admin/* or Director

app/services/auth.py

@@ -16,9 +16,18 @@ from app.core.security import (
 from app.models.user import User
 from app.schemas.auth import RegisterRequest
 
+# HARDENING.md P0.3 — least-privilege default for self-registered users.
+_SELF_REGISTER_ROLE = "CS Rep"
+
 
 async def register(db: AsyncSession, body: RegisterRequest) -> User:
-    """Create a new user.  Raises 409 if email already exists."""
+    """Create a new user.  Raises 409 if email already exists.
+
+    HARDENING.md P0.3: unauthenticated self-registration must never mint a
+    privileged role. The client-supplied ``role`` field is IGNORED — new
+    self-registered users always land on the least-privilege role.
+    Admins assign elevated roles directly (DB seed / admin endpoint).
+    """
     result = await db.execute(select(User).where(User.email == body.email))
     if result.scalar_one_or_none():
         raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="Email already registered")
@@ -28,7 +37,7 @@ async def register(db: AsyncSession, body: RegisterRequest) -> User:
         password_hash=hash_password(body.password),
         full_name=body.full_name,
         phone=body.phone,
-        role=body.role,
+        role=_SELF_REGISTER_ROLE,
     )
     db.add(user)
     await db.flush()