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/script.py.mako

@@ -0,0 +1,26 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+"""
+from __future__ import annotations
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}