fix(desktop): add artifact scanning for all 6 standalone experts in task panel

- Gateway paths (zhihu/wechat/content-planner) now do snapshot diff instead
  of hardcoded artifacts: [] — scan projectRoot + runtime/workspace/
- Handoff paths (geo workspace executor → gateway) now capture artifacts
  after the gateway call, not before when files haven't been generated yet
- Add collectWorkspaceExecutionArtifacts extraScanRoots parameter for
  scanning additional directories beyond projectRoot
- Exclude session-messages/ from artifact scanning to avoid false positives
- Add isWechatProject/isContentPlannerProject/isGeoProject helpers and
  extend resolveTaskPanelExpertName for 3 new expert name mappings
- Guard projectSkillRouter.resolve() behind bundled-runtime mode check
  to prevent "skills require bundled runtime" error in external-gateway mode
- Remove automation task panel recording (定时任务 excluded from workbench)
- UI: replace single douyin filter with per-expert artifact extension rules
  (expertArtifactExtensionRules), filter home-chat experts from workbench,
  restore 📦 emoji icon, update mock data for all 6 experts

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>