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/models.rs

@@ -57,24 +57,32 @@ pub struct Host {
 
 // ─── Port ─────────────────────────────────────────────────────────────────────
 
-/// A network port open on a host, with its likely protocol description.
+/// A network port entry in the global port catalog.
 ///
+/// Ports are defined once here; host_ports and application_ports link them
+/// to hosts and applications through separate join tables.
 /// Well-known ports (0–1023) have standardized protocol assignments.
-/// A port can be associated with multiple applications (non-strict relation).
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Port {
-    /// TCP/UDP port number.
-    /// `u16` is an unsigned 16-bit integer → range 0 to 65535,
-    /// which exactly matches the valid range for network ports.
+    /// TCP/UDP port number (0–65535).
+    /// `u16` is an unsigned 16-bit integer — the exact range for port numbers.
     pub number: u16,
 
-    /// Description of the likely protocol on this port.
-    /// `Option<String>`: may be absent (None) when the protocol is unknown.
+    /// Description of the protocol typically running on this port.
+    /// `Option<String>`: absent (None) when the protocol is unknown.
     /// Examples: Some("SSH"), Some("HTTPS"), None
     pub description: Option<String>,
+}
 
-    /// The host on which this port is open.
+// ─── HostPort ─────────────────────────────────────────────────────────────────
+
+/// Join record representing a port open on a specific host.
+///
+/// Maps to the `host_ports` table (many-to-many between hosts and ports).
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct HostPort {
     pub host_id: i64,
+    pub port_number: u16,
 }
 
 impl Port {