docs(examples): add usage examples for the WebSocket API

[FenjuFu]

What

Adds docs/examples.md - a practical "first conversation" guide for the WebSocket API - and links it from the documentation section of both READMEs.

Contents:

1. Start the engine - make run, default endpoint ws://localhost:8081/v1/ws
2. wscat smoke test - what the handshake looks like (session.event kind=opened), one user.message, what the card.* stream means
3. Minimal Node.js client - streaming text accumulation per (card_id, channel, index), the bare ping/pong keep-alive, auto-approving permission prompts, detecting turn completion via card.close on the turn card
4. Interrupting - session.interrupt with the observed trace_id
5. Prompt kinds table - valid decision values and reply payload shapes for permission / question / plan_review / step_decision
6. Reconnecting - session.resume with last_seq, and the prompt re-send / request_id dedup contract

Why

The protocol spec (docs/protocols/websocket.md) is thorough but is a wire contract, not a tutorial - there was no copy-paste path from "cloned the repo" to "saw streaming output". Usage examples are also the most-requested doc type from new integrators.

Verification

All frames, field names, decision values and defaults were taken from docs/protocols/websocket.md (v2 card model) and configs/config.yaml - notably the endpoint is /v1/ws per the spec, not the /ws currently shown in the README's protocol summary (that section also still says v1.4; happy to refresh it in a follow-up if wanted).

Docs-only change.

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.