Implement CE-WP-0004 T01-T05: citation card export (Markdown + HTML)

Per-evidence-item export: click Export → Copy as Markdown / Copy as HTML
writes a portable citation card to the clipboard. Cmd/Ctrl+Shift+C
exports the active evidence as Markdown.

- ADR-0007 locks the Markdown + HTML output formats.
- New shared types: CitationCard, openContextUrl(), resolveSourceLabel().
- Engine renderers under src/engine/rendering/: renderCitationCardMarkdown,
  renderCitationCardHtml — snapshot-tested, escape-safe, BEM classes for HTML.
- src/work/useExportEvidence.ts wires engine + renderers + clipboard.
- EvidenceSidebar gains an Export popover per row + auto-dismissing toast.
- E2E test (tests/integration/citation-card-export-e2e.dom.test.tsx)
  walks PRD scenario steps 10-11 and asserts the clipboard payload.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workplans/CE-WP-0004-citation-card-export.md

@@ -8,10 +8,10 @@ repo_id: a677c189-b4e2-4f2a-9e48-faa482c277e6
 topic_slug: citation_evidence_mvp
 topic_id: 96fa8e80-9f74-40f2-84cd-644e9747b9ec
 state_hub_workstream_id: 539919a4-f876-42b7-a28c-1a754c333139
-status: todo
+status: done
 owner: Bernd
 created: 2026-05-24
-updated: 2026-05-24
+updated: 2026-05-25
 depends_on_workplan: CE-WP-0002
 spec_refs:
   - wiki/ProductRequirementsDocument.md
@@ -52,7 +52,7 @@ T01 (CitationCard type + open-context URL convention)
 id: CE-WP-0004-T01
 state_hub_task_id: c15369da-0c42-4b5b-9d8c-cb91b316850f
 priority: high
-status: todo
+status: done
 ```
 
 Under `src/shared/`:
@@ -74,7 +74,7 @@ scheme stays the same.
 id: CE-WP-0004-T02
 state_hub_task_id: 4f94d27e-3727-4ad3-8f42-b0bb7ca74cb7
 priority: high
-status: todo
+status: done
 depends_on: [T01]
 ```
 
@@ -105,7 +105,7 @@ Unit tests: snapshot a few rendered cards against fixtures.
 id: CE-WP-0004-T03
 state_hub_task_id: 40c1aa86-64a1-4216-9e33-29fddf9c4d62
 priority: high
-status: todo
+status: done
 depends_on: [T01]
 ```
 
@@ -129,7 +129,7 @@ here — it ships in a later workplan.
 id: CE-WP-0004-T04
 state_hub_task_id: 0fa3c7e4-6868-4010-ade4-99a921ab0578
 priority: medium
-status: todo
+status: done
 depends_on: [T02, T03]
 ```
 
@@ -152,7 +152,7 @@ Markdown (the most common action).
 id: CE-WP-0004-T05
 state_hub_task_id: 8d1993b3-21a8-4be9-9ab1-29aa97e8301c
 priority: medium
-status: todo
+status: done
 depends_on: [T04]
 ```