feat(ui): map canvas follows light/dark theme; fix invisible gear control

The map view now selects a DARK_THEME or LIGHT_THEME palette from the
resolved app theme and threads it through every primitive builder, so
the canvas, planets, ship groups, cargo routes, battle/bombing markers,
fog, reach + selection rings, pending-Send tracks, and the pick overlay
all switch with the rest of the chrome. A theme flip remounts the
renderer preserving the camera — Pixi bakes the background at init and
every primitive bakes its colour at build, so a live re-tint is not
possible on the same instance.

This also fixes the reported bug: the gear-popover trigger and the
loading overlay hardcoded a dark navy background, so in light theme the
gear was invisible (dark icon on dark chip) until hover flipped it to a
white chip. Both now use the --color-surface-overlay token and read
correctly in both themes.

The light palette mirrors the dark one role-for-role, darkened /
saturated for contrast on a light background while keeping the incoming,
battle, and bombing accents vivid. The values are a first pass meant to
be refined during the F8 manual-QA loop.

Removes the now-dead "Phase 35" references from the code and lifts the
map-recoloring prohibition from the design-system / renderer docs; the
battle scene stays a fixed-palette data-viz surface.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ui/frontend/src/lib/i18n/index.svelte.ts

@@ -14,7 +14,7 @@
 // The locale state is exposed through a Svelte 5 runes singleton
 // (`i18n`) so components stay reactive without ceremony:
 // `<p>{i18n.t('login.title')}</p>` re-renders whenever
-// `i18n.locale` changes. Phase 35 will swap this primitive for a
+// `i18n.locale` changes. A later pass can swap this primitive for a
 // fuller solution once message-format pluralisation and lazy
 // loading become necessary.