fix(prefs): make the palette picker expand and scroll properly

[hanthor]

Show All Palettes did not expand the list: it collapsed it to a single
clipped row of three cards with no way to reach the other 241, and the
scroll wheel scrolled the page instead of the list.

The flow box was wrapped in a ScrolledWindow nested inside the
AdwPreferencesPage, which is already a scroller. A nested scrollable is
allocated its minimum height rather than its natural one, so
propagate-natural-height plus max-content-height never produced the
intended 480px viewport, and the inner scroller trapped the wheel. Drop
the wrapper and let the flow box grow in the group so the page scrolls
it, which is the native behavior and cannot trap scrolling.

Two more defects in the same picker:

• buildPaletteCSS added a fresh display-wide CSS provider on every
  call, and it is called on every expand/collapse, so a ~1200-rule
  stylesheet (244 palettes) was stacked on the display repeatedly,
  with every stale copy still matched against every widget. Reuse a
  single provider and reload its contents.

• Three of the eleven curated palette ids (high-contrast,
  solarized-dark, vs-code) matched no palette file, so the default
  view silently showed eight. Use the names the vendored collection
  actually uses, and place each curated entry at most once since that
  collection contains names differing only by case.

Verified against a real build under Xvfb: 11 featured cards, expand to a
readable scrollable grid of all 244, collapse back to 11, and clicking a
card still applies the palette.

Co-Authored-By: Claude Opus 5 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_014VCuQV4QC2zbUBDusaFift

[hanthor]

Closing — this PR is an artifact of the fork divergence, not a change to review.

hanthor/blueshell had drifted 5 commits ahead of and 25 commits behind tuna-os/blueshell, so this PR's diff is mostly the org repo's own commits appearing as if they were new. The one piece of original work in it, ci(flatpak): publish upstream Ghostty to the tuna-os remote, sync daily, has been superseded by tuna-os#83, which does the same job through the canonical reusable pipeline in tuna-os/.github instead of a bespoke 285-line workflow.

The rest of the fork's work has been salvaged into the org repo:

• Ghostty publishing → ci(flatpak): publish stock upstream Ghostty to the tuna-os remote tuna-os/blueshell#83 (merged)
• upstream-sync guards (the never-firing up-to-date check, and stacking sync PRs) → ci(upstream-sync): fix a short-circuit that could never fire, and don't stack sync PRs tuna-os/blueshell#84
• Site pages for BlueShell and Ghostty → docs: list BlueShell and Ghostty as apps on the site tuna-os/docs#373
• source-repo support in the shared publish pipeline → ci(flatpak): let a caller publish an app from another repo's source tuna-os/.github#75 (merged)

Not carried over: the fork's docs/TUNA_OS_PROMOTION.md rewrite, which recorded the org transfer as never having happened. It did happen, on 2026-08-17, and BlueShell has been live in the remote index since — the org repo's copy of that document was already correct.

hanthor/blueshell is being archived. Work continues at https://github.com/tuna-os/blueshell.