feat(reader): immersive chrome, slide-over drawers, tri-state PDF pointer mode

Phase 1 of the reader redesign:

- Reading surface is edge-to-edge; top/bottom bars overlay
  translucently (backdrop-blur) instead of reserving insets, killing
  the inset-coordination bug class entirely. Chrome auto-hides after
  2.5s of pointer inactivity (chrome_behavior setting finally wired:
  auto-hide / always-visible; legacy values map to auto-hide). Pointer
  activity inside page iframes keeps it awake; Esc toggles.
- TOC / Settings / Bookmarks become slide-over drawers with a scrim
  (z-50, full-height, safe-area aware), replacing the dockable-panel
  system and its window-shade headers. Only one drawer opens at a
  time; Esc or scrim click closes.
- Bottom bar is contextual: reflowable keeps nav/slider/progress/TOC;
  fixed-layout row adds Fit Page/Width select, zoom cluster,
  magnifier (now shows active state), Double Page Spread toggle, and
  a Smart | Pan | Text segmented control replacing the cryptic
  two-state icon. Smart = text-aware drag; Text = selection-only
  (manual smart-detect off); Pan = force pan. Choice persists via
  pdf_interaction_mode (new setting + foliate 29bc958 'text' mode).
- Settings drawer: Behavior (chrome, progress mode), Appearance with
  18 Kindle-style theme swatches (single source of truth from
  THEME_COLORS), Typography, Layout — each scoped by format.
- Keyboard: t/s/b open TOC/settings/bookmark, Esc closes drawers
  before toggling chrome, shortcuts skip form inputs; both slider
  rows tracked correctly (no duplicate-ID lookups).
- Topbar: Back, title, add-bookmark, bookmarks drawer, Aa settings;
  chrome follows user theme.

web/src/types/reader.d.ts

@@ -189,7 +189,7 @@ interface ReaderSettings {
   progress_mode: "pages" | "chapter" | "percentage" | "time-left";
 
   chrome_theme: string;
-  reading_theme: "light" | "sepia" | "dark" | "night" | "high-contrast";
+  reading_theme: string;
 
   reading_font:
     | "literata"
@@ -208,6 +208,7 @@ interface ReaderSettings {
   auto_scroll: boolean;
 
   double_page_spread: boolean;
+  pdf_interaction_mode: "select" | "pan" | "text";
   reading_direction: "ltr" | "rtl" | "vertical";
   reading_mode: "dark" | "light";