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

Dockerfile.api

@@ -0,0 +1,17 @@
+FROM golang:1.22-alpine AS build
+WORKDIR /src
+COPY go.mod ./
+RUN go mod download
+COPY . ./
+RUN go build -trimpath -ldflags='-s -w' -o /out/orchestra ./cmd/orchestra
+
+FROM alpine:3.21
+RUN adduser -D -u 10001 orchestra
+WORKDIR /app
+COPY --from=build /out/orchestra /app/orchestra
+COPY deploy/docker-api-entrypoint.sh /app/docker-api-entrypoint.sh
+RUN mkdir /data && chown orchestra:orchestra /data
+ENV ORCHESTRA_DATA=/data ORCHESTRA_PORT=9145
+VOLUME ["/data"]
+EXPOSE 9145
+ENTRYPOINT ["/app/docker-api-entrypoint.sh"]