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

internal/herdr/adapter.go

@@ -66,6 +66,13 @@ type AgentBlocker interface {
 type PaneCapture interface {
 	PaneCapture(context.Context, Session, string) (string, error)
 }
+
+// ApprovalResponder executes an explicitly displayed permission decision.
+// Implementations must re-read the pane before sending input so callers can
+// bind a decision to the exact capture they rendered.
+type ApprovalResponder interface {
+	RespondApproval(context.Context, Session, bool, string) error
+}
 type CLIAdapter struct {
 	Client  *Client
 	Harness string
@@ -595,6 +602,28 @@ func (a CLIAdapter) PaneCapture(ctx context.Context, s Session, source string) (
 	return r.Read.Text, nil
 }
 
+// RespondApproval only acts on harness prompts that visibly expose a y/n
+// choice. This deliberately refuses unknown dialog layouts rather than
+// guessing an Enter key could mean approval.
+func (a CLIAdapter) RespondApproval(ctx context.Context, s Session, grant bool, expectedCapture string) error {
+	current, err := a.PaneCapture(ctx, s, "recent")
+	if err != nil {
+		return err
+	}
+	if current != expectedCapture {
+		return fmt.Errorf("approval prompt changed")
+	}
+	low := strings.ToLower(current)
+	if !strings.Contains(low, "[y/n]") && !strings.Contains(low, "(y/n)") {
+		return fmt.Errorf("approval prompt has no unambiguous y/n confirmation")
+	}
+	input := "n\n"
+	if grant {
+		input = "y\n"
+	}
+	return a.Client.Call(ctx, "pane.send_text", map[string]any{"pane_id": s.PaneID, "text": input}, nil)
+}
+
 func statusFromAgentResult(v any) string {
 	if m, ok := v.(map[string]any); ok {
 		for _, key := range []string{"status", "agent_status", "state"} {