Shell 1.13.0: the Layouts menu lists the tiles a layout holds but the board is not showing, with a ✕ to remove each

A tile whose module stopped offering its picker entry — Slack's Send message
and Quick replies since the Send Message module took them over — kept its
place in the layout and drew nothing, as designed, but still held its grid
cells with no control anywhere to let them go: a dead area the operator
could not place anything in.

The Layouts menu now has a Not shown section, present only while the layout
holds such a tile. One row per tile: its title (or the module's name plus
the variant, or the module id when it is not installed), why in a few words
— "not offered right now", "module disabled", "module needs a newer
ProdDash", "module not installed" — and a drawn ✕ with a tooltip that
removes it, saves the layout and frees the cells, leaving the menu open as
the Grid Size stepper and Alerts do. The section repaints while the menu is
open whenever tiles become offered or stop being, and only when the list
changed. A tile that merely waits for its module keeps its place as before.

GET /api/modules also returns `inactive` — the installed modules that are
not running, id, name and reason only — so a dashboard can tell a disabled
module from one that is not installed. The toast after loading a named
layout now says the Layouts menu can remove the tiles it did not show.
README and the module guide updated.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

README.md

@@ -316,10 +316,15 @@ below. Nothing is installed without someone clicking.
   name, load a named layout (it becomes a local copy — browsers are never
   linked), or reset this browser's dashboard. Loading says what it did —
   *Loaded "FOH": 9 tiles, 2 not shown — Service, #ops aren't offered right
-  now* — with **Undo** in the message to get back the arrangement you had.
-  A tile whose module or picker entry isn't offered at the moment keeps its
-  place and shows nothing, then appears when it is; it is never replaced by
-  the module's default tile. Saving over an existing name asks first, and
+  now; the Layouts menu can remove them* — with **Undo** in the message to
+  get back the arrangement you had. A tile whose module or picker entry
+  isn't offered at the moment keeps its place and shows nothing, then
+  appears when it is; it is never replaced by the module's default tile.
+  While any tile is in that state the same menu has a **Not shown** section
+  listing each one with why — *not offered right now*, *module disabled*,
+  *module not installed* — and a ✕ that removes it and frees its cells, for
+  the tile that is not coming back (a module that stopped offering that
+  kind of tile). Saving over an existing name asks first, and
   the server keeps the copy it replaced: **Restore previous** in Admin →
   Saved layouts swaps it back (and swapping again undoes that). The menu's
   **Grid Size** stepper sets how many columns this browser cuts the board into —