Add master database with nodes, placements, and edge_routes

New internal/masterdb/ package for mcp-master cluster state. Separate
from the agent's registry because the schemas are fundamentally
different (cluster-wide placement vs node-local containers).

Tables: nodes, placements, edge_routes. Full CRUD with tests.
Follows the same Open/migrate pattern as internal/registry/.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/masterdb/db.go

@@ -0,0 +1,106 @@
+// Package masterdb provides the SQLite database for the mcp-master daemon.
+// It stores the cluster-wide node registry, service placements, and edge routes.
+// This is separate from the agent's registry (internal/registry/) because the
+// master and agent have fundamentally different schemas.
+package masterdb
+
+import (
+	"database/sql"
+	"fmt"
+
+	_ "modernc.org/sqlite"
+)
+
+// Open opens the master database at the given path and runs migrations.
+func Open(path string) (*sql.DB, error) {
+	db, err := sql.Open("sqlite", path)
+	if err != nil {
+		return nil, fmt.Errorf("open database: %w", err)
+	}
+
+	for _, pragma := range []string{
+		"PRAGMA journal_mode = WAL",
+		"PRAGMA foreign_keys = ON",
+		"PRAGMA busy_timeout = 5000",
+	} {
+		if _, err := db.Exec(pragma); err != nil {
+			_ = db.Close()
+			return nil, fmt.Errorf("exec %q: %w", pragma, err)
+		}
+	}
+
+	if err := migrate(db); err != nil {
+		_ = db.Close()
+		return nil, fmt.Errorf("migrate: %w", err)
+	}
+
+	return db, nil
+}
+
+func migrate(db *sql.DB) error {
+	_, err := db.Exec(`
+		CREATE TABLE IF NOT EXISTS schema_migrations (
+			version INTEGER PRIMARY KEY,
+			applied_at TEXT NOT NULL DEFAULT (datetime('now'))
+		);
+	`)
+	if err != nil {
+		return fmt.Errorf("create migrations table: %w", err)
+	}
+
+	for i, m := range migrations {
+		version := i + 1
+		var count int
+		if err := db.QueryRow("SELECT COUNT(*) FROM schema_migrations WHERE version = ?", version).Scan(&count); err != nil {
+			return fmt.Errorf("check migration %d: %w", version, err)
+		}
+		if count > 0 {
+			continue
+		}
+
+		if _, err := db.Exec(m); err != nil {
+			return fmt.Errorf("run migration %d: %w", version, err)
+		}
+		if _, err := db.Exec("INSERT INTO schema_migrations (version) VALUES (?)", version); err != nil {
+			return fmt.Errorf("record migration %d: %w", version, err)
+		}
+	}
+
+	return nil
+}
+
+var migrations = []string{
+	// Migration 1: cluster state
+	`
+	CREATE TABLE IF NOT EXISTS nodes (
+		name        TEXT PRIMARY KEY,
+		address     TEXT NOT NULL,
+		role        TEXT NOT NULL DEFAULT 'worker',
+		arch        TEXT NOT NULL DEFAULT 'amd64',
+		status      TEXT NOT NULL DEFAULT 'unknown',
+		containers  INTEGER NOT NULL DEFAULT 0,
+		last_heartbeat TEXT,
+		created_at  TEXT NOT NULL DEFAULT (datetime('now')),
+		updated_at  TEXT NOT NULL DEFAULT (datetime('now'))
+	);
+
+	CREATE TABLE IF NOT EXISTS placements (
+		service_name TEXT PRIMARY KEY,
+		node         TEXT NOT NULL REFERENCES nodes(name),
+		tier         TEXT NOT NULL DEFAULT 'worker',
+		deployed_at  TEXT NOT NULL DEFAULT (datetime('now'))
+	);
+
+	CREATE TABLE IF NOT EXISTS edge_routes (
+		hostname         TEXT PRIMARY KEY,
+		service_name     TEXT NOT NULL,
+		edge_node        TEXT NOT NULL REFERENCES nodes(name),
+		backend_hostname TEXT NOT NULL,
+		backend_port     INTEGER NOT NULL,
+		created_at       TEXT NOT NULL DEFAULT (datetime('now'))
+	);
+
+	CREATE INDEX IF NOT EXISTS idx_edge_routes_service
+		ON edge_routes(service_name);
+	`,
+}