Allow naming agents from the UI (add displayName + rename API)

[NitayRabi]

Motivation

• Provide a user-friendly, persistent display name for agents so operators can label agents in the UI without changing their internal ids.
• Expose a small control-plane API to let authenticated browser clients set/clear an agent's display name.
• Ensure the new field is persisted and surfaced in topology snapshots and the session-start UI.

Description

• Added an optional displayName to the shared protocol agentSchema and propagated it through the server model and responses.
• Persisted displayName in the DB with migration apps/server/drizzle/0001_agent_display_name.sql and wired it into apps/server/src/db/schema.ts.
• Implemented repository support: renameAgent(agentId, displayName) and ensured listTopology() / findAgent() return displayName.
• Added an authenticated endpoint PATCH /api/agents/:id in apps/server/src/app.ts that validates and normalizes input and broadcasts topology updates.
• Exposed renameAgent(...) in the browser API client (apps/web/src/api.ts) and updated AgentPicker UI (apps/web/src/components/AgentPicker.tsx) to show displayName ?? name and allow inline renaming via double-click.
• Updated tests and fixtures to cover the new behavior and added a server test renames an agent display name from browser API.

Testing

• Ran server unit/integration tests with cd apps/server && pnpm test -- --run test/app.test.ts and observed all tests passing (21 passed).
• Ran web tests with cd apps/web && pnpm test -- --run test/app.test.tsx and observed all tests passing (7 passed).
• Iterative test runs were used while adjusting imports and request validation until both suites passed.

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Codex Task