feat: add listSessions support to client and session

[varin-nair-factory]

Description

Add listSessions() method to DroidClient and DroidSession, enabling programmatic session listing with cursor-based pagination via the droid.list_sessions JSON-RPC method.

Changes

• src/schemas: Add ListSessionsRequestParamsSchema, SessionInfoSchema, ListSessionsResultSchema, request/response schemas, re-export from barrel
• src/client.ts: Add listSessions(params?) method to DroidClient — skips _ensureSession() so it works before session init
• src/session.ts: Add listSessions(params?) method to DroidSession
• Tests: Schema validation tests, client send/parse tests (with and without params, no session required), session delegation test, throws-after-close guards

Usage

// From a session
const session = await createSession({ cwd: "/my/project" });
const { sessions, nextCursor } = await session.listSessions({ cwd: "/my/project" });

// From a client (no session required)
const client = new DroidClient({ transport });
const result = await client.listSessions();

Key Design Decisions

• No session required: listSessions skips _ensureSession() so it works before initializeSession or loadSession
• Optional cwd filter: when provided, scopes to that project; when omitted, returns all sessions
• Cursor-based pagination: nextCursor in the response for paginating through large session lists

Related CLI PR

https://github.com/Factory-AI/factory-mono/pull/12082

Related Issue

part of FAC-18627