[Nacho1499]

Closes #448

What does this PR do?

Adds a separate practice mode with unlimited attempts, guidance, instant feedback, replay, difficulty adjustment, and non-ranked progress tracking.

Type of change

• New feature (non-breaking change that adds functionality)

How was it tested?

• Unit tests added/updated
• [ ]
  npm test -- --runInBand src/game-engine/tests/practice-mode.service.spec.ts — passed (10 tests).
  npx eslint on the changed files — passed.
  npx prettier --check on the changed files — passed.
  npm run typecheck -- --incremental false --pretty false — failed due to existing type errors in unrelated files; no practice-mode errors were reported.

No manual curl verification was performed.

Checklist

[x] I added/updated tests for the change

• I added a changeset / migration if schema changed
• I read CONTRIBUTING.md

Screenshots / Logs

Focused unit test result: 1 suite passed, 10 tests passed.

Risk & rollout

Adds practice-session and practice-attempt tables. Apply the included database migration before enabling the practice endpoints. Existing ranked puzzle creation remains unchanged; practice attempts earn no rewards and do not affect ranked progress.

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