feat(db): add SQLx migrations and AppState with connection pool

- Add sqlx 0.8 (AnyPool, runtime-tokio, sqlite, postgres, migrate)
- Create 6 migration files for both SQLite and PostgreSQL backends
- Add server/db.rs: create_pool and run_migrations helpers
- Add server/state.rs: AppState with LeptosOptions + AnyPool
- Run migrations at server startup before accepting requests
- Fix Port model: remove host_id (ports are now a global catalog)
- Add HostPort join struct for the host_ports many-to-many table

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

migrations/sqlite/0001_create_networks.sql

@@ -0,0 +1,6 @@
+-- networks: IP address ranges managed by the IPAM.
+-- Each network has a unique CIDR block (e.g. "192.168.1.0/24").
+CREATE TABLE IF NOT EXISTS networks (
+    id   INTEGER PRIMARY KEY AUTOINCREMENT,
+    cidr TEXT    NOT NULL UNIQUE
+);