Remove vendored plugins/agent-connect; consume upstream via extends #35

Part of the agent-connect upstream batch (T2 of 5).

Blocked by: #34

What it delivers

Zero local agent-connect code in this repo. The plugin comes from the parent runtime; this repo only wires its secrets and dependency edges.

Scope

• Delete plugins/agent-connect/ (vendored copy of feat(agents): agent-connect plugin — owner-controlled agent accounts on the NEAR Intents Agent API NEARBuilders/everything-dev#403)
• Drop the path override from the agent-connect entry in bos.app.ts; keep the secrets list (NEAR_INTENTS_AGENT_API_KEY, AGENT_CONNECT_ENCRYPTION_KEY, AGENT_CONNECT_DATABASE_URL)
• Keep connectors.dependsOn: ["agent-connect"]
• bos types gen so the generated plugin client includes the upstream agent-connect contract
• Verify the connectors bridge still composes: plugins["agent-connect"] in-process client and agentTransfer (plugins/connectors/src/index.ts) resolve against the upstream contract — the contract is identical to the vendored copy per the drift kit, so no rework is expected

Acceptance

• plugins/agent-connect/ deleted; rg "agent-connect" finds only config/secrets references
• Connectors integration tests green (agent bridge mocked as today)
• pnpm run typecheck and pnpm run test green
• App behavior unchanged; agent-connect still dormant