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.

internal/services/reader.go

@@ -392,18 +392,19 @@ func (s *ReaderService) UpdateSettings(
 
 func (s *ReaderService) getDefaultSettings() map[string]interface{} {
 	return map[string]interface{}{
-		"chrome_behavior":    "auto-hide",
-		"progress_mode":      "pages",
-		"chrome_theme":       "tokyo-night",
-		"reading_theme":      "dark",
-		"reading_font":       "literata",
-		"font_size":          16,
-		"line_height":        1.6,
-		"margin_width":       20,
-		"tap_zone_size":      30,
-		"auto_scroll":        false,
-		"panel_zoom_enabled": true,
-		"double_page_spread": true,
+		"chrome_behavior":      "auto-hide",
+		"progress_mode":        "pages",
+		"chrome_theme":         "tokyo-night",
+		"reading_theme":        "dark",
+		"reading_font":         "literata",
+		"font_size":            16,
+		"line_height":          1.6,
+		"margin_width":         20,
+		"tap_zone_size":        30,
+		"auto_scroll":          false,
+		"panel_zoom_enabled":   true,
+		"double_page_spread":   true,
+		"pdf_interaction_mode": "select",
 
 		// Dockable panel defaults
 		"panel_layout": map[string]interface{}{