feat: add wiki issue cross references

[zhangyangyu]

Description

Adds wiki pages as issue and pull request cross-reference sources. When wiki content mentions a compatible issue, pull request, or URL target, the service records wiki-origin references and surfaces cross-referenced events on target timelines with wiki source payloads. Catalog sync keeps create, update, rename, delete, and cleanup paths aligned while existing repository visibility checks still gate timeline events.

Tracking

N/A

Tests

• make check
• go test ./internal/rest ./internal/service

SSOT Drift Prevention Checklist

• Checked that this PR does not violate boundaries in docs/architecture.md or docs/module-contracts.md
• Package structure and dependencies are unchanged; no SSOT doc update needed
• Test conventions and coverage expectations are unchanged; no docs/test-strategy.md update needed
• CI, smoke, regression, and packaging workflows are unchanged; no docs/ci.md update needed