feat(server): mint API + Postgres schema + manual adapter (PR 1)

Source-agnostic license issuance service. FastAPI app fronts a
Postgres `licenses` table; the only currently-wired source is
`manual` (operator mints via /internal/mint). Gumroad webhook
adapter lands in PR 2.

Key design points:

- Signing reuses src/license/crypto.py via a COPY into the image
  (single source of truth — blobs minted server-side verify against
  the same embedded pubkey on the buyer's machine).
- Source adapter Protocol (app/adapters/base.py) is the seam for
  Gumroad / Lemon Squeezy / Stripe in later PRs; Mint API speaks
  only SaleEvent / RefundEvent.
- (source, source_order_id) UNIQUE composite gives idempotent
  webhook retries without double-mint.
- JSONB type uses with_variant(JSON, 'sqlite') so the same models
  drive both Postgres prod and SQLite tests (no testcontainers dep).
- Bearer-token auth on /internal/*; the IP-loopback guard was
  removed after the docker bridge made it fight legitimate prod
  traffic (nginx defense + Bearer remain).
- Secrets resolved via *_FILE env vars pointing at
  /run/secrets/<name>, so passwords never appear in `docker inspect`.

21 unit tests (SQLite in-memory, StaticPool) plus a real-Postgres
docker-compose smoke test in server/scripts/smoke.sh that builds the
image, runs the alembic migration, mints a license, verifies the
signature against the host dev pubkey, and checks the DB row.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/alembic/env.py

@@ -0,0 +1,46 @@
+"""Alembic environment.
+
+Reads the runtime database URL from ``app.db`` (which resolves the
+password from the secrets file), so ``alembic upgrade head`` Just
+Works inside the API container with no extra env wiring.
+"""
+
+from __future__ import annotations
+
+from logging.config import fileConfig
+
+from alembic import context
+
+from app.db import Base, engine
+from app import models  # noqa: F401 — imported for side-effect of registering models
+
+config = context.config
+
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+target_metadata = Base.metadata
+
+
+def run_migrations_offline() -> None:
+    context.configure(
+        url=str(engine.url),
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online() -> None:
+    with engine.connect() as connection:
+        context.configure(connection=connection, target_metadata=target_metadata)
+        with context.begin_transaction():
+            context.run_migrations()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()