Upgrade to @minigraf/browser 3.x at the v3.0.0 release #47

The playground depends on @minigraf/browser ^2.0.6. When Minigraf v3.0.0 is published, move to 3.x and bring the tutor prompt and lessons in line with v3. An audit on 2026-10-24 ran every lesson step and every docs and tutor-prompt snippet on v2.0.10 and on the v3 branch (949813ce). It found no changed answers; every step matches its expectedResult on both. The prompt changes below come from that audit.

• Bump @minigraf/browser to ^3.0.0.
• Tutor system prompt (lib/system-prompt.ts):
  • The v3 pseudo-attribute rule: :db/tx-count, :db/valid-from and the like read the nearest earlier pattern on the same entity, otherwise PRS-081 (minigraf#594).
  • An unknown aggregate or window function is QRY-010 / QRY-011. On v2.x it returns []. The geomean example needs updating.
  • The syntax template's parse error is now PRS-087 (it was INT-019).
  • The v3.0.0 answer changes listed under Breaking changes in the core CHANGELOG (minigraf#551): or-branch not sees expression bindings, and an unknown predicate in a not body is QRY-007 when the query opens. Plus the spec §4 changes.
• Re-run the lesson audit against 3.x: every step runs without error and matches expectedResult.
• Revert the sl3-s4 workaround ((transfer-chain ?club ?dest) [(= ?dest :rovers)] in lib/lessons/tutorial-sports-league.ts) to (transfer-chain ?club :rovers). minigraf#608 was fixed in v2.0.7, but the lockfile pinned @minigraf/browser 2.0.6, so the revert also needs the dependency bump. Both are in fix(lessons): revert the sl3-s4 workaround for minigraf#608; @minigraf/browser 2.0.10 #48 (^2.0.10); done in fix(lessons): revert the sl3-s4 workaround for minigraf#608; @minigraf/browser 2.0.10 #48.

Related: #40 (other lesson workarounds).