feat(07.3-02): ES256 JWT algorithm upgrade + startup rotation hook

- config.py: add refresh_token_expire_hours=16, jwt_private_key, jwt_public_key fields (D-01, D-09)
- services/auth.py: swap all 4 JWT sites to ES256 via base64-decoded PEM keys; remove HS256 (D-02, D-03)
- main.py: add _rotate_tokens_on_algorithm_change lifespan hook — bulk-revokes refresh tokens on algorithm change; idempotent on repeat boots (D-04, D-05)
- test_auth_es256.py: promote ES256-01..05 + CFG-01 stubs to 6 passing tests; RM-01..03 remain xfail
- docker-compose.yml: inject JWT_PRIVATE_KEY + JWT_PUBLIC_KEY into backend + celery-worker (D-07)
- README.md: add JWT key env vars + key generation Python one-liner snippet
- .env.example: add JWT_PRIVATE_KEY= and JWT_PUBLIC_KEY= lines
- Version bump to 0.1.2

README.md

@@ -140,7 +140,9 @@ Copy `.env.example` to `.env`. Only the fields marked **Required** must be set b
 
 | Variable | Description |
 |----------|-------------|
-| `SECRET_KEY` | JWT signing secret — generate with `openssl rand -hex 32` |
+| `SECRET_KEY` | Legacy HMAC secret (kept for future use) — generate with `openssl rand -hex 32` |
+| `JWT_PRIVATE_KEY` | base64-encoded PEM PKCS8 private key for ES256 JWT signing (required) |
+| `JWT_PUBLIC_KEY` | base64-encoded PEM SubjectPublicKeyInfo public key for ES256 JWT verification (required) |
 | `CLOUD_CREDS_KEY` | Master key for cloud credential encryption — generate with `openssl rand -hex 16` (pad to 32 chars) |
 | `ADMIN_EMAIL` | Bootstrap admin email |
 | `ADMIN_PASSWORD` | Bootstrap admin password (must pass strength check) |
@@ -159,6 +161,29 @@ Copy `.env.example` to `.env`. Only the fields marked **Required** must be set b
 | `GOOGLE_CLIENT_ID/SECRET` | *(unset)* | Required only if using Google Drive backend |
 | `ONEDRIVE_CLIENT_ID/SECRET` | *(unset)* | Required only if using OneDrive backend |
 
+### JWT Key Generation
+
+Phase 7.3 uses ES256 (ECDSA P-256) asymmetric signing. The private key signs tokens; the public key verifies them. A leaked public key cannot forge tokens.
+
+Generate the keypair with a single Python command:
+
+```bash
+python3 -c "
+from cryptography.hazmat.primitives.asymmetric import ec
+from cryptography.hazmat.primitives import serialization
+import base64
+k = ec.generate_private_key(ec.SECP256R1())
+priv = base64.b64encode(k.private_bytes(serialization.Encoding.PEM, serialization.PrivateFormat.PKCS8, serialization.NoEncryption())).decode()
+pub  = base64.b64encode(k.public_key().public_bytes(serialization.Encoding.PEM, serialization.PublicFormat.SubjectPublicKeyInfo)).decode()
+print(f'JWT_PRIVATE_KEY={priv}')
+print(f'JWT_PUBLIC_KEY={pub}')
+"
+```
+
+Paste the two output lines into your `.env` file at the project root.
+
+> **Warning:** Rotating these keys invalidates every active session — the startup rotation hook will bulk-revoke all refresh tokens on the next boot.
+
 ---
 
 ## Development