feat(tiles): Tile Animations setting, entrance styles for the tile grid

Tiles become the fifth entrance surface (data-tile-anim), switched on in App
Settings > Appearance > Tile Animations and OFF by default: the default is the
grid's own quick fade (`settle`), exactly as before.

A styled tile plays in two beats: its frame enters as it mounts (fly out of
its session tab, dealt from the Tiles button, CRT power-on, beam down from its
tab, cascade, pop, soft), and its screen then plays the terminal pane style of
the entrance theme when its first capture lands, through the same
html[data-term-anim] rules on .tile-body. Each style has its own exit when the
Tiles button closes the grid (back into the tabs, a CRT switch-off, ...).

Picking an Entrance Animations theme presets the tile style (new Launch theme:
tiles fly from the tabs); the theme readout ignores the tile row, so changing
it never shows "Custom". Frames move transform and opacity only (one fit and
one PTY resize per tile), a reload's restore always settles, and nothing moves
under reduced motion. The lab (?animlab=1) gets a Tile grid group, a cascade
order picker and in-place replay / close + reopen.

Also removes the terminal pane's `boot` entrance style (owner decision); a
saved `boot` falls back to off.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/tile-grid-plan.md

@@ -97,7 +97,10 @@ or settled a question the spec left open. The invariants as built are in
   `test/header-icon-hover.test.ts`.
 - **The grid opens and closes with a short animation, on by default** (owner request:
   "when clicking on the tile button first make this animation nicer"). It is the grid's
-  own, not an `entrance-animations.js` theme (those are off by default). Opening, each tile
+  own `settle` style, the default of App Settings → Appearance → Tile Animations, which
+  switches on other styles (`fly` out of the tabs, `deal` from the Tiles button, `crt`,
+  `beam`, ...; docs/architecture-invariants.md#entrance-animations).
+  Opening, each tile
   fades and settles in (opacity, translateY 6px and scale .97), 180 ms, 24 ms apart in
   reading order (`--tile-enter-index`): the last of six is done at 300 ms; a tile added
   later enters the same way. Its terminal stays transparent (`.tile--revealing`) until the