v0.3.0: I'm stuck help, teach-before-test, fairer bosses

A way out when the kid gets stuck, teaching before testing, and bosses that are fair.

Added

• "I'm stuck 🤔" button next to Check on every graded question, boss battles included. Each tap goes one step
  further: a hint, then a worked example of a similar problem plus how to start this one, then "Skip for now".
  Skipping costs no heart, points or streak; in a boss it's neither a hit nor a miss. New POST /api/stuck and
  POST /api/skip (Worker and Node server).
• Typing "idk", "I don't know", "dunno", "no idea", "help", "skip", "don't show this"… in a fill-in opens the
  same help instead of being graded wrong.
• Deterministic scaffolds (src/stuck.js, no live AI): worked steps for fraction → decimal/percent (halving,
  money, ×10/100/1000), fraction of a number, adding/multiplying/dividing fractions, simplifying and whole-number
  facts, plus fair nudges for mc/order/match/true-false/number line/fraction bar. Packs can supply their own
  steps and example.
• Teach before test. New learn card type (idea + worked example, revealed one step per tap) and guided
  practice ("guided": true + steps, shown before answering). In Play, a new or shaky math skill now gets a
  generated Learn-it card and 2 guided items before it's graded.
• "Boss ahead! Here's your power-up" recap card before every boss (quest bosses: the stage's powerup, or the
  earlier learn card; Play bosses: the skill's idea + a worked example).
• Support tracking: stuck / skipped events in the day log; per-topic support in progress; skipped items are
  re-queued for a day later, guided and never as a boss. export-progress.mjs adds stuck/skipped to
  weakSpots, plus needsSupport and requeued; the parent report counts them.
• Validator rules (publish-lessons.mjs): a new skill's stage must start with a learn/why card and a guided
  question; a boss may only test skills taught/practised earlier in the quest (teaches) or mastered; no boss answers
  past thousandths or with decimal percents. --offline skips the progress lookup.
• Tests: test/stuck.test.mjs (stuck → hint → example → skip on the 3/16 boss, fair bosses, retry cap,
  validator rules, and an end-to-end run on the Node server).

Changed

• Play bosses are fair and can't trap the kid: a boss only appears after the skill has 2 right answers, its level is
  capped at 4, generated boss questions never need more than 3 decimal places (no more 3/16 = 0.1875 in a boss), a
  question the kid missed or skipped isn't generated again for a day, and two boss misses pause that boss until tomorrow
  and re-teach the skill first.
• The example quest follows teach → guided → graded → boss (new "Fraction Training Cove" stage before the Kraken).
• LESSONS.md and docs/NIGHTLY.md: the teach → guided practice → graded → boss rule and the gentle "stuck" deep dive.
• Dependencies: wrangler 4.149.0 → 4.151.1 (devDependency; brings workerd/miniflare 1.20261006.1 → 1.20261012.1).
  The UI libs (Motion 14.3.0, Floating UI 1.8.0, canvas-confetti 1.9.4, AutoAnimate 0.10.0) and esbuild 0.28.2 were
  already the latest; the vendor bundle was rebuilt. npm audit: 0 vulnerabilities.

Dependencies: wrangler 4.149.0 → 4.151.1 (dev). UI libs and esbuild already latest; npm audit: 0 vulnerabilities.

Full changes: v0.2.0...v0.3.0 · PR #1