Icon topbar, module title-bar controls, hideable title bars, renames

Topbar: the add button is now just ＋ and the layout button a 3-segment
grid icon (two squares + one tall rectangle). Modules no longer build
their own toolbars — moduleApi.header.addButton/addMenu put controls in
the tile's title bar next to the gear/close (menus are fixed-positioned
by the shell so a tile's overflow can't clip them, and everything a
module adds is removed automatically on unmount). Each title bar grows a
notch on its bottom edge that hides/shows the bar, ProdCom-Listener
style; the choice persists with the layout. Modules renamed: ProdCom and
ProPresenter. The ProdCom tile regains the original listener tools as
icon buttons in its title bar: timestamps toggle (clock), A−/A+ text
size, jump-to-latest, and a circle-with-cross clear button, plus the
Channels menu. MODULE-GUIDE documents the header API; README updated.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RNYUv9EyrGSFmCnmH7WYKH

modules/prodcom-transcript/module.json

@@ -1,6 +1,6 @@
 {
   "id": "prodcom-transcript",
-  "name": "ProdCom Transcript",
+  "name": "ProdCom",
   "version": "1.0.0",
   "description": "Live ProdCom transcript stream",
   "client": "client.js",