Phase 2: SQLite persistence, admin setup-link, login/sessions

Implements the secure single-admin panel entry (spec 7.6).

- internal/store: modernc.org/sqlite (pure Go, static build), WAL +
  foreign keys, embedded PRAGMA user_version migrations; schema 0001
  covers admin/settings/domains/applications/send_log/rate_limits (spec 9).
- Setup secret-link (spec 7.6.1): 128-bit crypto/rand token, printed to
  log + /data/setup-token (0600), 10-min TTL with regeneration, per-IP
  rate limit, subtle.ConstantTimeCompare, failures don't invalidate,
  one-time admin form, permanent invalidation once admin exists (/setup 404).
- bcrypt admin password; server-side username/password validation.
- Login + in-memory sessions, crypto-random token, cookie
  HttpOnly/Secure/SameSite (Secure toggleable for dev HTTP), login
  rate limit, auth middleware.
- html/template base layout + setup/login/dashboard, vendored htmx 2.0.4.
- build/entrypoint.sh: fix bind-mounted /data ownership as root before
  supervisord drops to the unprivileged panel user (found via container test).

Verified on selfpost.example.com: go vet/build/test/gofmt clean; e2e curl
of setup+login flows; docker build + run with -v ./data:/data creates the
DB and 0600 token owned by panel.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/store/store.go

@@ -0,0 +1,100 @@
+// Package store owns the SelfPost SQLite database: the single file under /data
+// that persists the administrator account, sending domains and applications,
+// the send log and rate-limit settings (spec 9). It exposes typed queries so
+// the rest of the panel never builds SQL by hand.
+package store
+
+import (
+	"database/sql"
+	"embed"
+	"fmt"
+	"io/fs"
+	"sort"
+
+	_ "modernc.org/sqlite" // pure-Go SQLite driver (no cgo), keeps the static build
+)
+
+//go:embed migrations/*.sql
+var migrationsFS embed.FS
+
+// Store wraps the database connection pool.
+type Store struct {
+	db *sql.DB
+}
+
+// Open opens (creating if needed) the SQLite database at path, enables WAL and
+// foreign keys, and applies any pending migrations. The caller owns Close.
+func Open(path string) (*Store, error) {
+	// _pragma parameters are applied on every pooled connection by the driver,
+	// so foreign-key enforcement and WAL survive connection churn.
+	dsn := fmt.Sprintf("file:%s?_pragma=journal_mode(WAL)&_pragma=busy_timeout(5000)&_pragma=foreign_keys(ON)", path)
+	db, err := sql.Open("sqlite", dsn)
+	if err != nil {
+		return nil, fmt.Errorf("open database: %w", err)
+	}
+	// modernc's driver serializes writes anyway; a small pool avoids
+	// "database is locked" surprises under WAL.
+	db.SetMaxOpenConns(1)
+
+	s := &Store{db: db}
+	if err := s.migrate(); err != nil {
+		db.Close()
+		return nil, err
+	}
+	return s, nil
+}
+
+// Close closes the underlying database.
+func (s *Store) Close() error {
+	return s.db.Close()
+}
+
+// migrate applies embedded migrations in filename order, tracking progress via
+// SQLite's PRAGMA user_version so each migration runs at most once.
+func (s *Store) migrate() error {
+	entries, err := fs.ReadDir(migrationsFS, "migrations")
+	if err != nil {
+		return fmt.Errorf("read migrations: %w", err)
+	}
+	names := make([]string, 0, len(entries))
+	for _, e := range entries {
+		if !e.IsDir() {
+			names = append(names, e.Name())
+		}
+	}
+	sort.Strings(names)
+
+	var version int
+	if err := s.db.QueryRow("PRAGMA user_version").Scan(&version); err != nil {
+		return fmt.Errorf("read schema version: %w", err)
+	}
+
+	for i, name := range names {
+		target := i + 1
+		if target <= version {
+			continue
+		}
+		sqlBytes, err := migrationsFS.ReadFile("migrations/" + name)
+		if err != nil {
+			return fmt.Errorf("read migration %s: %w", name, err)
+		}
+		tx, err := s.db.Begin()
+		if err != nil {
+			return fmt.Errorf("begin migration %s: %w", name, err)
+		}
+		if _, err := tx.Exec(string(sqlBytes)); err != nil {
+			tx.Rollback()
+			return fmt.Errorf("apply migration %s: %w", name, err)
+		}
+		// PRAGMA does not accept a bound parameter, and target is a trusted
+		// loop index, so formatting it in is safe.
+		if _, err := tx.Exec(fmt.Sprintf("PRAGMA user_version = %d", target)); err != nil {
+			tx.Rollback()
+			return fmt.Errorf("bump schema version for %s: %w", name, err)
+		}
+		if err := tx.Commit(); err != nil {
+			return fmt.Errorf("commit migration %s: %w", name, err)
+		}
+	}
+	return nil
+}