fix(rmi-backend): drop passlib — route backup codes through direct bcrypt

The reported symptom (AttributeError: module 'bcrypt' has no attribute
'__about__') was misleading. passlib 1.7.4 (the latest released version
— the project is unmaintained) actually traps that AttributeError with
a bare `except:` and continues. The real failure occurs later in
`passlib.handlers.bcrypt._finalize_backend_mixin`:

  detect_wrap_bug -> verify(secret, bug_hash)
    where secret = (b"0123456789"*26)[:255]   # 255-byte test secret

bcrypt 4.0+ removed silent 72-byte truncation and now raises
`ValueError: password cannot be longer than 72 bytes`, breaking the
backend probe and crashing every `pwd_context.hash()/verify()` call.

Three options were considered:

  A. Upgrade passlib — impossible, 1.7.4 is the latest PyPI release.
  B. Pin bcrypt<4.0  — conflicts with chromadb 1.1.1 (>=4.0.1 required),
     even though chromadb's bcrypt usage is optional and still works
     at runtime in practice.
  C. Shim bcrypt.__about__ — doesn't fix the actual truncation error.

Chosen: refactor app/auth.py to use bcrypt directly for backup-code
hashing too (the main `hash_password`/`verify_password` already did).
Drops the passlib dependency entirely, restoring bcrypt 5.x for chromadb
compatibility and eliminating the unmaintained passlib pin.

Verified:
  * hash_password / verify_password round-trip OK
  * _hash_backup_code / _verify_backup_code round-trip OK on
    freshly generated 8-digit backup codes
  * `pytest tests/unit` -> 717 passed, 32 warnings, 60 subtests passed

app/auth.py

@@ -12,9 +12,9 @@ import secrets
 from datetime import datetime, timedelta
 from typing import Any
 
+import bcrypt
 from fastapi import APIRouter, HTTPException, Request
 from jose import JWTError, jwt
-from passlib.context import CryptContext
 from pydantic import BaseModel, Field
 
 from app.core.redis import get_redis
@@ -86,12 +86,12 @@ def _generate_backup_codes(count: int = 8) -> list:
 
 def _hash_backup_code(code: str) -> str:
     """Hash a backup code for storage (same as password hashing)."""
-    return pwd_context.hash(code)
+    return hash_password(code)
 
 
 def _verify_backup_code(code: str, hashed: str) -> bool:
     """Verify a backup code against its hash."""
-    return pwd_context.verify(code, hashed)
+    return verify_password(code, hashed)
 
 
 # ── Config ──
@@ -99,10 +99,6 @@ JWT_SECRET = os.getenv("JWT_SECRET", "rmi-jwt-secret-change-me")
 JWT_ALGORITHM = "HS256"
 JWT_EXPIRY_DAYS = 7
 
-import bcrypt  # noqa: E402
-
-pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
-
 
 def hash_password(password: str) -> str:
     """Hash password using bcrypt directly."""

app/routers/bulletin.py

@@ -31,7 +31,7 @@ from app.services.supabase_service import (  # noqa: E402
 )
 
 
-# Lazy auth dependency - avoids importing passlib+jose+bcrypt at module load
+# Lazy auth dependency - avoids importing jose+bcrypt at module load
 async def _require_public_profile(request: Request):
     from app.auth import require_public_profile