Fix sheet peek for async content, and rework several screens' details

showNooSheet's peek detection previously measured content once, right
after the first frame - Details' Versions/Activity tabs fetch their
data asynchronously, so that one-shot measurement only ever saw the
initial loading-spinner height, never the eventual (often long) list,
and the sheet still snapped to full height once data arrived. Replaced
it with a ScrollMetricsNotification-based check that keeps content
capped at the peek height from frame one and upgrades to a draggable
sheet whenever it actually overflows that cap, however and whenever
that happens - fixed for good this time, with a regression test that
mirrors the async-load shape.

Also, in the same pass:
- Upload/Move/Copy's bottom bar meta line now always reads as a count
  ("Uploading 3 items"), never a filename for the single-item case,
  and is centered rather than left-aligned - matches the approved
  design and removes a bespoke marquee/chip implementation that only
  Upload had.
- Upload/Move/Copy now show the same FilesControlsRow (sort, filter,
  List/Grid) Files itself uses, including a folder-grid rendering
  path for when List/Grid is set to grid.
- Files' filter chip reads "Filters" instead of "All types" when idle.
- Trash's overflow button - whose only action is "Delete forever" -
  is now a direct delete icon (mobile) / "Delete" danger pill
  (desktop) instead of a generic "..." menu that hid a single action
  behind an extra tap.
- The media viewer's floating chrome (top bar, bottom action bar,
  video transport row) now follows the app's light/dark theme instead
  of a fixed dark panel - a dark panel read as out of place over a
  light-theme stage. Panel tint and icon/text colors come from the
  theme's own surface/fg1 tokens (at a higher blur opacity to stay
  legible over arbitrary photo/video brightness), and the edge scrim
  gradients fade toward the panel's own tint instead of a fixed black.
  Mirrored the same change into the design canvas's Main.dc.html/
  MainAndroid.dc.html mockups (now with a theme prop) so they match.

.claude/context/design-system/DESIGN_SYSTEM.md

@@ -343,13 +343,16 @@ Sidebar items are 38px tall with radius 12, an 18px icon and a 14/500 label. The
 - **Media viewer** (the full-screen photo/video viewer): the stage is `bg`,
   following the app's own theme rather than a fixed black - a black stage
   in light mode read as jarringly out of place. A translucent, blurred top
-  bar (back, filename, meta) and bottom bar float over the media in a fixed
-  dark panel regardless of theme (it needs to read over arbitrary photo/
-  video brightness, not over `bg`); this is the one deliberate exception to
-  "no blur" in product UI, since it's chrome over photo/video content, not
-  over the app's own surfaces. Both bars' background extends edge-to-edge
-  behind the status bar/gesture area, with only their content padded clear
-  of it. Back is a plain arrow (`arrow-left`), not the iOS
+  bar (back, filename, meta) and bottom bar float over the media in a
+  `surface`-tinted panel (also theme-following, at a higher opacity than a
+  typical blur so it stays legible over arbitrary photo/video brightness
+  underneath - icons/text are `fg1`, matching); this is the one deliberate
+  exception to "no blur" in product UI, since it's chrome over photo/video
+  content, not over the app's own surfaces. A short edge gradient outside
+  each panel (toward `surface`, not a fixed black) extends that same
+  contrast a little past the panel's hard edge. Both bars' background
+  extends edge-to-edge behind the status bar/gesture area, with only their
+  content padded clear of it. Back is a plain arrow (`arrow-left`), not the iOS
   chevron+label pushed-screen pattern - platform split still to do. The
   bottom bar holds every action in one row (share, favorite, open
   externally, download, delete, details) on every platform; don't add a
@@ -369,10 +372,13 @@ Sidebar items are 38px tall with radius 12, an 18px icon and a 14/500 label. The
 - **Upload / Move / Copy destination picker:** a pushed screen (outside the
   tab shell, so it carries its own complete top bar) titled "Upload to" /
   "Move to" / "Copy to". Back arrow (Android) or "Cancel" text (iOS) leading,
-  no trailing action. Breadcrumb row, then a folder-only list (no files: this
-  screen only browses folders) using the standard file row/tile at the
-  folder kind. Bottom bar: a meta line ("Moving 3 items") above a full-width
-  52px primary CTA ("Upload here" / "Move here" / "Copy here").
+  no trailing action. The same `FilesControlsRow` (sort chip, filter chip,
+  List/Grid toggle right-anchored) Files itself uses, then a breadcrumb row,
+  then a folder-only list/grid (no files: this screen only browses folders)
+  using the standard file row/tile/grid-card at the folder kind. Bottom bar:
+  a centered meta line ("Moving 3 items") above a full-width 52px primary
+  CTA ("Upload here" / "Move here" / "Copy here") - a count, never a
+  filename, even for a single item.
 
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