feat: workspace aliases, tab groups of split panes, native path picker (v2.1.0)

- /api/workspaces and `agenthub workspace(s)` / `--workspace` as aliases of
  /api/lanes and `agenthub lanes` / `--lane`; old names print one stderr note.
  REPL `help lanes|workspace|workspaces` resolves through the aliases.
- A workspace holds up to ten sessions (slots 0-9); every console tab is a
  group of 1-4 split panes (PaneGroups, agenthub.workspace.paneLayout);
  parseGroups keeps the stored active tab when an earlier one is dropped.
- Browse button beside path fields: POST /api/lanes/pick-path opens the OS
  picker on the server's desktop — loopback only and no forwarding header
  (EREMOTE), a display failure is ENODIALOG not a Cancel, the dialog is
  killed when the request closes, a folder field falls back to the in-app
  browser on any failure.
- Changes rail counts chip, image viewer (/git/raw), status bar session
  counts and per-day cost (`date=` on /api/pricing/cost).
- /agenthub-open and /agenthub-doctor run from the INSTALLED build
  (supersededBy), doctor offers fixes behind two confirmations; plugin-open
  treats a locked bootstrap as non-fatal.
- New-terminal shell waits for the first attach (issue #55).
- repo-onboarding / debug-live-issue skills removed.
- OpenAPI: pick-path, lane/date on /pricing/cost, tool on /run/history,
  /api/workspaces mount.

client/src/components/RemoteSources.tsx

@@ -86,6 +86,7 @@ import { toast } from "../lib/toast";
 import { isRemoteDataRefreshMessage } from "../lib/remoteDataEvents";
 import { useDataScope } from "../lib/dataScope";
 import type { ScopeMode } from "../lib/dataScope";
+import { PathPickButton } from "./PathPickButton";
 
 /** Data-scope choices in display order (the radio group's arrow-key order). */
 const SCOPE_MODES: ScopeMode[] = ["all", "local", "selected"];
@@ -558,12 +559,19 @@ export function RemoteSources() {
               <label className="block text-xs text-fg-muted mb-1">
                 {t("remoteSources.fieldIdentity", "Identity file (optional)")}
               </label>
-              <input
-                className="input w-full font-mono"
-                placeholder="~/.ssh/id_ed25519"
-                value={form.identity_file ?? ""}
-                onChange={(e) => setForm((f) => ({ ...f, identity_file: e.target.value }))}
-              />
+              <div className="flex gap-1.5">
+                <input
+                  className="input w-full font-mono"
+                  placeholder="~/.ssh/id_ed25519"
+                  value={form.identity_file ?? ""}
+                  onChange={(e) => setForm((f) => ({ ...f, identity_file: e.target.value }))}
+                />
+                <PathPickButton
+                  kind="file"
+                  start={form.identity_file || "~/.ssh"}
+                  onPick={(p) => setForm((f) => ({ ...f, identity_file: p }))}
+                />
+              </div>
             </div>
             <div className="sm:col-span-2">
               <label className="block text-xs text-fg-muted mb-1">