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/main.py

@@ -83,10 +83,17 @@ app = FastAPI(
     lifespan=lifespan,
 )
 
-# ── CORS ─────────────────────────────────────────────────────────────
+# ── CORS (HARDENING.md P0.2 — explicit origin allow-list, never "*") ──
+_origins = [o.strip() for o in settings.CORS_ORIGINS.split(",") if o.strip()]
+if "*" in _origins or not _origins:
+    raise RuntimeError(
+        "CORS_ORIGINS must be an explicit comma-separated origin allow-list "
+        "(e.g. 'https://denya.sysloggh.net,http://localhost:8000'). "
+        "'*' with allow_credentials=True is invalid and unsafe. Refusing to start."
+    )
 app.add_middleware(
     CORSMiddleware,
-    allow_origins=settings.CORS_ORIGINS.split(",") if settings.CORS_ORIGINS != "*" else ["*"],
+    allow_origins=_origins,
     allow_credentials=True,
     allow_methods=["*"],
     allow_headers=["*"],