Add TCP/UDP port mapping support

- Add app_ports table for storing port mappings per app
- Add Port model with CRUD operations
- Add handlers for adding/deleting port mappings
- Add ports section to app detail template
- Update Docker client to configure port bindings when creating containers
- Support both TCP and UDP protocols

internal/database/migrations/003_add_ports.sql

@@ -0,0 +1,12 @@
+-- Add port mappings for apps
+
+CREATE TABLE app_ports (
+    id INTEGER PRIMARY KEY,
+    app_id TEXT NOT NULL REFERENCES apps(id) ON DELETE CASCADE,
+    host_port INTEGER NOT NULL,
+    container_port INTEGER NOT NULL,
+    protocol TEXT NOT NULL DEFAULT 'tcp' CHECK(protocol IN ('tcp', 'udp')),
+    UNIQUE(host_port, protocol)
+);
+
+CREATE INDEX idx_app_ports_app_id ON app_ports(app_id);