Reader: visible text selection in every theme; highlights follow across translations

Selection
- Selected text uses a per-theme colour (it was nearly invisible on Dark)
- The colour picker also appears on touch screens after dragging the selection
  handles, and sits below the selection there so the system menu doesn't cover it

Highlights
- Each highlight remembers its translation and whether it covers the whole verse
- In another translation the same words are found again (ignoring case and
  punctuation); whole-verse highlights cover the whole verse; when the wording
  differs, the verse gets a small colour dot instead of marking the wrong words
- Older highlights are checked against their saved words instead of trusted
- Server keeps the new fields

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/index.css

@@ -19,8 +19,9 @@ body {
   color: #0f172a;
 }
 
+/* Selected text follows the reading theme, so it stays visible on dark as well as light pages. */
 ::selection {
-  background: rgba(15, 23, 42, 0.18);
+  background: var(--r-sel, rgba(15, 23, 42, 0.18));
 }
 
 button,