fix(cert): A2B success_criteria as {id,text} objects (unbreak main)

[bokelley]

Summary

• Migration 478 (A2B hands-on lab, docs(learning): add A2B hands-on lab module — Testing Your First Agent #3398) shipped exercise_definitions[].success_criteria as plain strings.
• SuccessCriterion is { id, text } (server/src/db/certification-db.ts:48-51), and server/tests/integration/demonstrations-fairness.test.ts:105 asserts every criterion has an id.
• As a result, Server integration tests has been failing on main since docs(learning): add A2B hands-on lab module — Testing Your First Agent #3398 merged — confirmed on run 25856546952. All open PRs (mine included: fix(admin): full IANA timezone list in events + meetings forms #4532) are blocked behind this.
• Migration 479 converts each string criterion to {id: "<exercise_id>_c<n>", text: <string>}. Idempotent — CASE WHEN jsonb_typeof = 'string' skips entries already in object form, so re-running is safe and any future hand-edits to objects survive.

Verification

• Applied 478 + 479 against a fresh local Postgres.
• Verified 12 criteria across a2b_ex1..a2b_ex4 now render as {id, text} with ids a2b_ex1_c1, a2b_ex1_c2, …, a2b_ex4_c3.
• vitest run server/tests/integration/demonstrations-fairness.test.ts → 13/13 pass locally (was 12/13 with the same DB pre-479).

Test plan

• CI: Server integration tests green
• Spot-check A2B module in /learning still renders exercises correctly post-migration

🤖 Generated with Claude Code