fix(docs): address PR #92 review comments

- Fix D-134 cross-references to point to architecture.md (not content.md)
- Fix stale #620 reference in D-147 body (now #679)
- Fix content.md footer count (44, not 45)
- Add D-145, D-146, D-147 to decisions/README.md index
- Add Q-WTF-041 entry to questions-content.md (was referenced but untracked)
- Fix sprint-28-candidates.md totals line
- Align spelling to British "customisation" throughout new decisions
- Add information boundary classification to D-147 (public trait, per D-010)
- Add "first message" instruction to proposer rules in sprint-start skill

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/sprints/sprint-28/sprint-28-candidates.md

@@ -28,7 +28,7 @@ These tickets have: team assigned, no unresolved open questions, no upstream blo
 | **#624** | Quietly responsive world | server | World Feel | No blockers. Proximity-weighted NPC attention + reaction systems. |
 | **#625** | Dual-scale consequence model | server | World Feel | No blockers. Sharp events + slow accumulation. Rimworld + DF model. |
 
-**Total:** 7 tickets across server (3), client (1), planning (2), + 1 server unblocking ticket
+**Total:** 7 tickets across server (4), client (1), planning (2)
 
 ---