release: 0.1.0: Phases 0-11: panel, Postfix/DKIM, milter, backup, Docker image

Initial feature-complete implementation of the v1.0 specification (phases 0-11 of `docs/implementation-plan.md`).
Added:
  - Panel (Go, single static binary) with SQLite persistence, one-time
  - Domain management with per-domain DKIM (RSA-2048, generated in pure Go) and
  - Application (sender identity) management: SASL credentials via `sasldb2`,
  - Full Postfix relay config generated from env at container start: SMTPS 465,
  - Journal milter (pure Go, `go-milter`) recording every send to `send_log`;
  … (6 more in CHANGELOG)

Full detail: CHANGELOG.md (0.1.0).

internal/store/migrations/0002_sessions.sql

@@ -0,0 +1,12 @@
+-- Panel login sessions (spec 7.6.6, plan B.1). Persisted so a login survives a
+-- container restart or redeploy; only the SHA-256 of the session token is
+-- stored, never the token itself, so a stolen database file cannot be used to
+-- sign in. expires_at implements the sliding idle timeout: it is pushed
+-- forward on activity rather than being fixed at creation time.
+CREATE TABLE sessions (
+    token_hash TEXT PRIMARY KEY,
+    username   TEXT NOT NULL,
+    created_at TEXT NOT NULL,
+    expires_at TEXT NOT NULL
+);
+CREATE INDEX idx_sessions_expires_at ON sessions (expires_at);