Add web UI and worker capture/approval command channel

Introduces the browser-facing surface and the worker-side protocol that
backs it:

- internal/ui: joined read model plus per-task lifecycle and approval
  controls, kept separate from the raw endpoints workers and harnesses
  depend on.
- internal/webui + web/: Vite/React app, build output embedded via
  go:embed and served as an SPA fallback.
- federation: per-(worker, task) captures with a monotonic revision that
  advances only when pane text actually changes, and a command queue
  restricted to grant_approval / deny_approval, each bound to the capture
  revision the operator acted on.
- orchestra-worker: publishes captures and executes commands only after
  re-reading the pane and confirming the revision still matches. Sends
  keystrokes only for a visible y/n prompt or OpenCode's fully labelled
  selector, and refuses to deny through that selector rather than guess
  at unobservable navigation.

This is the ownership boundary AUDIT.md's B14 and B17 call for: approval
becomes an explicit, revision-bound operation executed by the worker that
owns the pane, instead of a side effect of prompting over a
coordinator-driven remote socket.

Also ignores the web build inputs and outputs. node_modules ships vendored
Go packages, so go build and go test walk into it if it is merely
untracked; both node_modules and .node_modules are excluded.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01535A3Y8RtkAi8wYuWhtkEd

web/src/api/client.ts

@@ -0,0 +1,5 @@
+import type { Detail, Overview } from './types'
+async function request<T>(path:string, init?:RequestInit):Promise<T>{const r=await fetch(path,{headers:{'Content-Type':'application/json',...init?.headers},...init});if(!r.ok)throw new Error(await r.text());return r.json() as Promise<T>}
+async function text(path:string){const r=await fetch(path);if(!r.ok)throw new Error(await r.text());return r.text()}
+async function upload(body:string){const r=await fetch('/v1/artifacts',{method:'POST',headers:{'Content-Type':'text/markdown'},body});if(!r.ok)throw new Error(await r.text());return (await r.json() as {ref:string}).ref}
+export const api={overview:()=>request<Overview>('/v1/ui/overview'),detail:(id:string)=>request<Detail>('/v1/ui/tasks/'+id),artifact:(ref:string)=>text('/v1/ui/artifacts/'+ref),upload,create:(body:unknown)=>request('/v1/ui/tasks',{method:'POST',body:JSON.stringify(body)}),action:(id:string,action:string,body={})=>request<Detail>(`/v1/ui/tasks/${id}/actions/${action}`,{method:'POST',body:JSON.stringify(body)})}