make sidebar filter boxes CLI-addressable via the MessageBus (T-270)

The sidebar/dock filter fields (the shared ClideFilterBox) had no CLI
peer — a one-way, UI-only affordance that broke D-6 parity. Add the
drive+observe verb `clide ui filter <address> [<text>]`, routed entirely
through the kernel MessageBus pub/sub so a box reacts to a published
message identically whether the trigger was a UI keystroke or the CLI —
keeping extensions first-class (no dispatcher→widget wiring).

- ClideFilterBox gains an `address`; when set it listens on `filter.set`
  for its address and republishes its value on `filter.state`. Null
  address keeps the box a kernel-free UI widget.
- FilterStateCache (new kernel service) caches the latest `filter.state`
  per address — the bus has no retention, so this backs the observe-half.
- ui.filter: with text → publishes `filter.set` (drive); without →
  reads the cache (observe). Honest toolError when there is no live UI.
- Address every box: decisions/tickets/files/git/output/problems panes,
  the four search boxes, and the pql search/query/markdown inputs.

Addresses are the ids from `clide pane list` (e.g. decisions.panel).
settings.json: allow the `clide` CLI + relevant skills.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/builtin/git/src/git_panel_view.dart

@@ -75,7 +75,7 @@ class _GitPanelViewState extends State<GitPanelView> {
           explicitChildNodes: true,
           child: Column(
             children: [
-              ClideFilterBox(hint: 'Filter changes…', onChanged: (v) => setState(() => _filter = v)),
+              ClideFilterBox(address: 'git.panel', hint: 'Filter changes…', onChanged: (v) => setState(() => _filter = v)),
               Expanded(
                   child: SingleChildScrollView(
                 padding: const EdgeInsets.symmetric(vertical: 4),