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>

CHANGELOG.md

@@ -18,6 +18,13 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
 
 ### Added
 
+- The sidebar/dock **filter boxes are now CLI-addressable** (D-6 parity): `clide
+  ui filter <address> <text>` drives a pane's filter exactly as typing in it
+  would, and `clide ui filter <address>` reads the current value back. Addresses
+  are the box ids from `clide pane list` (e.g. `decisions.panel`, `files.tree`,
+  `search.findInFiles`). Routed entirely through the MessageBus pub/sub — a box
+  reacts to a published `filter.set` the same whether the trigger was a click or
+  the CLI, keeping extensions first-class. (T-270)
 - Click an inline image card to open it in a full-screen **lightbox** — zoom
   (scroll/pinch), pan, double-click to reset, `Esc`/backdrop to dismiss — since
   the cards are often too small to read. `clide image show <path> --fullscreen`