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>

src/server/db.rs

@@ -0,0 +1,68 @@
+// server/db.rs — Database connection pool and migrations
+//
+// This module provides two functions called once at server startup:
+//   - `create_pool`    : opens a connection pool to the database
+//   - `run_migrations` : applies all pending SQL migrations
+//
+// `AnyPool` lets the same Rust code target both SQLite (dev) and
+// PostgreSQL (production) — only DATABASE_URL changes.
+
+use sqlx::AnyPool;
+use thiserror::Error;
+
+use crate::server::config::{AppConfig, DatabaseBackend};
+
+// ─── Errors ───────────────────────────────────────────────────────────────────
+
+#[derive(Debug, Error)]
+pub enum DbError {
+    #[error("Database connection failed: {0}")]
+    Connection(#[from] sqlx::Error),
+
+    #[error("Migration failed: {0}")]
+    Migration(#[from] sqlx::migrate::MigrateError),
+}
+
+// ─── Pool creation ────────────────────────────────────────────────────────────
+
+/// Opens a connection pool to the database specified in `config.database_url`.
+///
+/// A pool maintains multiple open connections so concurrent requests
+/// do not block each other waiting for a single connection.
+///
+/// `install_default_drivers()` must be called before `AnyPool::connect`
+/// to register both the SQLite and PostgreSQL drivers in the `Any` registry.
+pub async fn create_pool(config: &AppConfig) -> Result<AnyPool, DbError> {
+    // Register SQLite and PostgreSQL drivers so `AnyPool` can dispatch
+    // to the correct one based on the URL scheme (sqlite:// vs postgres://).
+    sqlx::any::install_default_drivers();
+
+    let pool = AnyPool::connect(&config.database_url).await?;
+    Ok(pool)
+}
+
+// ─── Migrations ───────────────────────────────────────────────────────────────
+
+/// Applies all pending migrations from the directory matching the active backend.
+///
+/// Two separate directories handle SQL syntax differences:
+///   - `migrations/sqlite/`   : uses `INTEGER PRIMARY KEY AUTOINCREMENT`
+///   - `migrations/postgres/` : uses `BIGSERIAL PRIMARY KEY`
+///
+/// SQLx tracks applied migrations in a `_sqlx_migrations` table, so running
+/// this function on an already-migrated database is always safe (idempotent).
+///
+/// `sqlx::migrate!("path")` is a compile-time macro: it embeds all `.sql`
+/// files from the given path directly into the binary. The path is relative
+/// to the project root (where Cargo.toml lives).
+pub async fn run_migrations(pool: &AnyPool, backend: &DatabaseBackend) -> Result<(), DbError> {
+    match backend {
+        DatabaseBackend::Sqlite => {
+            sqlx::migrate!("migrations/sqlite").run(pool).await?;
+        }
+        DatabaseBackend::Postgres => {
+            sqlx::migrate!("migrations/postgres").run(pool).await?;
+        }
+    }
+    Ok(())
+}