chore(07.3-02): wire JWT env vars in docker-compose, README key-gen, .env.example, bump to 0.1.2

- docker-compose.yml: add JWT_PRIVATE_KEY + JWT_PUBLIC_KEY to backend and celery-worker service env blocks
- README.md: add JWT_PRIVATE_KEY/JWT_PUBLIC_KEY to required env vars table; add JWT Key Generation section with Python one-liner and warning about session revocation
- .env.example: add JWT_PRIVATE_KEY= and JWT_PUBLIC_KEY= adjacent to SECRET_KEY
- backend/main.py: version bump 0.1.1 -> 0.1.2
- frontend/package.json: version bump 0.1.1 -> 0.1.2

.env.example

@@ -31,6 +31,11 @@ REDIS_URL=redis://:changeme_redis@redis:6379/0
 # JWT signing secret — generate with: python3 -c "import secrets; print(secrets.token_hex(64))"
 SECRET_KEY=CHANGEME-replace-with-64-char-random-hex
 
+# ── JWT Key Pair (Phase 7.3 — ES256) ─────────────────────────────────────────
+# Generated by running the Python snippet in README.md JWT Key Generation section
+JWT_PRIVATE_KEY=
+JWT_PUBLIC_KEY=
+
 # ── Admin Bootstrap (Phase 2 — D-04) ─────────────────────────────────────────
 # First admin account created on startup if users table is empty.
 # Both vars must be set; if missing, a WARNING is logged but app starts normally.