refactor(v2): remove trigger_credential_collection MCP tool

Drops the in-chat credential-collection flow introduced in e92b245. Agents
can no longer collect API keys via a secure modal — users must add secrets
through OneCLI directly. Keeps the OneCLI manual-approval handler and
threaded-routing work from the same commit intact.

Removed:
* container/agent-runner/src/mcp-tools/credentials.ts (MCP tool)
* src/credentials.ts (host-side modal/OneCLI pipeline)
* src/db/credentials.ts + migration 005 (pending_credentials table)
* src/onecli-secrets.ts (createSecret CLI facade, only caller was credentials.ts)
* findCredentialResponse from agent-runner DB layer
* PendingCredential types
* Four credential hooks from ChannelSetup (getCredentialForModal,
  onCredentialReject, onCredentialSubmit, onCredentialChannelUnsupported)
* Credential card/modal handling in chat-sdk-bridge (nccr/nccm prefixes,
  Modal/TextInput imports)
* credential_request text fallback in WhatsApp adapter
* request_credential system-action case in delivery.ts

Added:
* Migration 009 drops pending_credentials on existing installs.

Vercel skill now tells the agent to ask the user to register the token via
OneCLI instead of invoking the removed tool.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/channels/adapter.ts

@@ -27,14 +27,6 @@ export interface ChannelSetup {
 
   /** Called when a user clicks a button/action in a card (e.g., ask_user_question response). */
   onAction(questionId: string, selectedOption: string, userId: string): void;
-
-  /** Credential collection hooks — used by chat-sdk-bridge to route the modal flow. */
-  getCredentialForModal?(
-    credentialId: string,
-  ): { name: string; description: string | null; hostPattern: string } | null;
-  onCredentialReject?(credentialId: string): void;
-  onCredentialSubmit?(credentialId: string, value: string): void;
-  onCredentialChannelUnsupported?(credentialId: string): void;
 }
 
 /** Inbound message from adapter to host. */