feat(provider): add github copilot device flow provider (#364)

db/migrations/0062_github_copilot_user_oauth.down.sql

@@ -0,0 +1,21 @@
+-- 0062_github_copilot_user_oauth (rollback)
+-- Remove user-scoped provider OAuth tokens and github-copilot client type.
+
+DROP INDEX IF EXISTS idx_user_provider_oauth_tokens_state;
+DROP TABLE IF EXISTS user_provider_oauth_tokens;
+
+DELETE FROM providers WHERE client_type = 'github-copilot';
+
+ALTER TABLE IF EXISTS providers DROP CONSTRAINT IF EXISTS providers_client_type_check;
+
+ALTER TABLE IF EXISTS providers
+  ADD CONSTRAINT providers_client_type_check CHECK (
+    client_type IN (
+      'openai-responses',
+      'openai-completions',
+      'anthropic-messages',
+      'google-generative-ai',
+      'openai-codex',
+      'edge-speech'
+    )
+  );