Fix pull-to-refresh, header tint, sheet controls, and Shares tap

- Every tab's RefreshIndicator+CustomScrollView was missing an explicit
  AlwaysScrollableScrollPhysics, so pull-to-refresh silently couldn't be
  triggered once the list was short enough to fit the viewport (empty,
  or a single item) - the platform default physics only allows the
  overscroll drag RefreshIndicator listens for once content overflows.
- StickyHeaderDelegate (Files'/Photos'/Favorites' pinned controls row)
  painted its background from Theme.of(context).colorScheme.surface -
  Flutter's own Material 3 scheme, reseeded by the user's accent color
  choice - instead of context.nooColors.bg like the rest of the screen,
  showing as a stray colored cast behind the row.
- NooSegmentedControl gains onSurface: true wherever one sits inside a
  sheet (Files'/Photos' sort and type-filter controls) - it defaulted to
  the same surface fill as the sheet itself, so the control had no
  visible boundary showing it as a grouped unit.
- Shares tab: removed the per-row "..." overflow menu on every scope
  (With you/By you/Links); tapping a row now opens the full Share sheet
  for that item instead, fetched via the new
  FilesController.fetchItemAtPath (a share only carries enough metadata
  for its own row, not what the sheet's header needs).
- fetchShares() now reuses _shareFromJson instead of its own thinner
  inline parser, so url/token/permissions/expireDate are actually
  populated - a public-link share could never show "Copy link" before.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.claude/context/styling.md

@@ -96,6 +96,24 @@ Gotchas:
   trigger it; a full swipe never deletes.
 - Window chrome (macOS traffic lights, the Windows 40px title bar) isn't
   built yet. `NooSidebar.windowControls` is the slot for it.
+- Always read colors through `context.nooColors`, never
+  `Theme.of(context).colorScheme` - the latter is Flutter's own Material 3
+  scheme, reseeded by the user's accent color choice (`AppTheme.light`/
+  `.dark`), so anything painted from it carries a faint hue of whatever
+  accent is picked instead of the app's neutral palette. `sticky_header_delegate.dart`
+  shipped with this bug once already (a pinned controls-row header tinted
+  by the accent instead of matching its screen's plain `colors.bg`).
+- `NooSegmentedControl` defaults to `onSurface: false` (`colors.surface`
+  fill) - right when it's sitting directly on `colors.bg` (List/Grid
+  toggle, Shares' scope switcher), but pass `onSurface: true` for one
+  placed inside a sheet or dialog (already `colors.surface`), or its pill
+  track blends invisibly into the sheet instead of reading as a grouped
+  control (Files'/Photos' sort and type-filter sheets do this).
+- Any `RefreshIndicator` needs `physics: const AlwaysScrollableScrollPhysics()`
+  on its scrollable child, or pull-to-refresh silently can't be triggered
+  once the list is short enough to fit the viewport (empty, or one item) -
+  every tab's `CustomScrollView` sets this explicitly for exactly that
+  reason.
 
 ## Reusable chrome