feat(gateway): add runtime chat interface

[HayronHgh]

What

Adds a browser-first Runtime Chat Gateway for Context OS without turning llama.cpp into the agent runtime.

Browser
  → Context OS Gateway :8787
  → RuntimeSession (one AgentRuntime per session)
  → tools / evidence / memory / context
  → shared LlamaClient
  → llama-server :8080
  → Qwen

• Adds a dependency-free Node HTTP gateway and responsive vanilla HTML/CSS/JS UI.
• Adds session creation, turn execution, SSE event replay, and a browser approval bridge.
• Keeps conversation history and tool authority inside Runtime; the Browser holds presentation state only.
• Exposes Runtime-derived evidence metadata so the UI does not mislabel every successful tool call as durable.
• Adds Windows start/stop launchers and bilingual English/Traditional Chinese documentation.
• Advances the development version to 0.2.0-dev.6.

API

• POST /api/sessions
• GET /api/sessions/:id
• DELETE /api/sessions/:id
• POST /api/sessions/:id/turn
• GET /api/sessions/:id/events (SSE)
• POST /api/sessions/:id/approvals/:approvalId
• GET /api/health
• GET /api/config

Runtime and security boundary

• One AgentRuntime per session; the LlamaClient and llama-server are shared.
• Single-flight turns and one active session per canonical project root.
• Runtime-issued, single-use, fail-closed approval IDs.
• Loopback-only listener, Host/Origin checks, JSON content-type and body limits.
• Restrictive CSP, no CORS exposure, no inline script, and text-only model rendering.
• Bounded SSE replay history (256 events / 2 MiB).
• Whole session state remains Runtime-owned; only the opaque session ID is stored in Browser local storage.

Deliberate stops

This milestone does not:

• proxy or embed the llama.cpp Web UI;
• grant llama.cpp built-in filesystem/tool authority;
• wire the frozen D0–D6 transformation pipeline into interactive turns;
• add token streaming, LAN exposure, or authentication;
• change frozen planner/proposal/validation/execution experiment inputs.

The interactive chain stops at the existing deterministic AgentRuntime turn loop.

Validation

• npm test: 185 tests, 184 passed, 0 failed, 1 skipped (Windows symlink capability/EPERM only).
• JavaScript syntax, JSON parsing, PowerShell parsing, git diff --check: passed.
• 118 local Markdown links checked: passed.
• Secret-pattern and unsafe DOM/CORS/bind-pattern audits: clean.
• Frozen M4 and D0–D6 core paths: unchanged.
• Real in-app browser + live Qwen/llama.cpp smoke:
  • Qwen requested read_file; the tool trace and answer were rendered correctly.
  • Qwen requested a write; the approval card was shown, Deny was enforced, and no file was created.
  • Browser console: 0 warnings/errors.

Review status

Draft freeze candidate for 0.2.0-dev.6 — Runtime Chat Gateway.