Bug fixes:
- loadSettings() now uses ?? instead of ||, so a legitimately saved 0
  (e.g. "Number of sets: 0") survives reopening the popup
- The alliteration letter is now picked via getAlliterationCandidates()
  from letters covered by every content list of the active theme, so no
  draw ever needs the silent off-letter fallback; the entropy letter
  pool uses the real candidate count instead of a flat 26
- The crack-scenario listener reads the stored lastEntropy value
  instead of regex-parsing "(N bits)" out of the display text

Housekeeping:
- Retire stale internal docs (.claude/claude.md, .claude/TODO.md,
  .claude/SENTENCE_ANALYSIS.md, docs/RELEASE_NOTES_v1.1.md); open
  roadmap ideas are salvaged into the root TODO.md
- Add homepage_url to manifest.json
- 5 new tests for getAlliterationCandidates (109 total)