feat(gamification): Phase 3 — 38 new achievements + triggers + 'exam' group

Adds achievement coverage for every feature shipped since the original
seed: exam-prep (math9), textbooks, classroom/board, biochemistry,
live-quiz, flashcards, hangman/crossword, pet, plus a new 'social' group
for class & leaderboard wins and 'consistency' extensions (streak_100,
goal_30, early_bird, night_owl).

74 achievements now (was 36), grouped into 7 sections:
  onboarding (3) → volume (8) → mastery (16) → consistency (7) →
  exam (9) → exploration (21) → social (10)

A new top-level group 'exam' slots between consistency and exploration
in the profile UI.

What's wired in service.checkPhase3Achievements (called from
checkAchievements):
  • streak_100 — extends the existing streak track
  • goal_30 — 30 days with daily_goals fully met (SUM check)
  • early_bird / night_owl — strftime('%H', xp_log.created_at)
  • exam_first / 25 / 100 — exam_attempts where is_correct=1
  • exam_variant_clear / 5_variants — perfect mock-variant sessions
  • exam_topic_master — ≥10 attempts at ≥90% on a single subtopic
  • exam_mock_done / pass / perfect — exam_mock_sessions.score
  • tb_first_para — textbook_progress
  • fc_first_deck / 100_cards / 1000_cards — flashcard_reviews
  • bc_first_molecule / 5_challenges / 20_challenges — bio_user_*
  • game_win_5 / 25 — xp_log reason IN (hangman_win, crossword_win)
  • pet_streak_7 / 30 — users.pet_petting_streak
  • lq_first / 3_quizzes — live_answers grouped by session
  • cr_first_join / 5 / 25_lessons — classroom_attendance
  • class_5_members / 25 — teacher's biggest class
  • parent_link — parent_links presence
  • lb_top10 / lb_top1 — weekly XP rank among students

What's deferred (catalog entry only, no trigger yet):
  • tb_chapter_done / tb_book_done / tb_3_books — need to parse
    textbook_progress.paragraphs_read JSON against textbook structure

Every block is wrapped in its own try/catch so a missing table on a
legacy install can't take down the whole achievement sweep.

Verified end-to-end: admin user picked up 7 new unlocks on first
checkAchievements call after seed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/profile.html

@@ -1724,6 +1724,7 @@
     { slug: 'volume',      title: 'Объём',         icon: 'bar-chart-2' },
     { slug: 'mastery',     title: 'Качество',      icon: 'award' },
     { slug: 'consistency', title: 'Постоянство',   icon: 'flame' },
+    { slug: 'exam',        title: 'Экзамен 9',     icon: 'clipboard-list' },
     { slug: 'exploration', title: 'Исследование',  icon: 'compass' },
     { slug: 'social',      title: 'Социальное',    icon: 'users' },
   ];