fix(kb): search preview shows section-in-context for text sources

User reported the search card "looks broken" when the selected hit is the
law (Wikisource source 5) — the right preview pane just duplicates the
chunk text already visible in the left list card. For PDF sources the
right pane shows the PDF page, but for text-only sources it had nothing
useful to add and fell back to a copy.

Fix:
- /kb/search hits gained chunk_index (shira-hermes b127caf), and
  /kb/source/{id}/chunks gained an `around=<chunk_index>&ctx=<k>` window.
- Espo proxy plumbing: getActionChunks reads `around`/`ctx` query
  params and forwards them; KnowledgeBaseService::sourceChunks accepts
  optional $around + $ctx and appends them to the upstream URL.
- showSearchPreview for non-PDF hits now fetches the matched chunk plus
  2 sections before and 2 after, renders them as stacked panels: the
  matched section gets a yellow #fff3cd highlight, neighbors render as
  muted context blocks. The panel header carries a prominent
  "פתח ב-Wikisource" button so users can jump to the public source page.
  After render the matched section auto-scrolls into view.
- Race protection via _previewToken: a click on a different hit while a
  fetch is in flight cancels the stale render so the user always sees
  the section that matches the currently-selected card.

PDF path unchanged.

Refs Task Master #7

.taskmaster/tasks/tasks.json

@@ -37,6 +37,18 @@
         "dependencies": [],
         "createdAt": "2026-04-25T10:00:00Z"
       },
+      {
+        "id": 7,
+        "title": "fix: search preview duplicates left card for text sources",
+        "description": "User report: searching the law (Wikisource source 5) shows the same chunk content in both the left list-card and the right preview pane. The preview adds zero value when the matched source has no PDF — both panes are visually identical (modulo the left's 14em truncation), which reads as a bug. Fixed by fetching the matched chunk plus K=2 surrounding sections from /kb/source/{id}/chunks?around=N&ctx=2 and rendering them stacked: matched section is highlighted with a yellow header (#fff3cd), neighbors render as muted context blocks above and below. Adds a prominent 'פתח ב-Wikisource' button in the panel header, scrolls the matched section into view on render. Race-safe via _previewToken so a quick second click doesn't render stale results.",
+        "status": "done",
+        "priority": "high",
+        "details": "shira-hermes b127caf added chunk_index to /kb/search hits + an `around`/`ctx` query param to /source/{id}/chunks. Espo controller passes them through. Client uses the new fields in showSearchPreview when the hit is a text source.",
+        "testStrategy": "Search 'מהי תקנה 36'; click the law-kind hit. Right pane: yellow-highlighted ס' 36 in the middle, ס' 35 above (muted), ס' 37 below (muted), Wikisource button in header. Click the תקנה 37 חוזר hit: right pane swaps to PDF iframe at the cited page (PDF path unchanged).",
+        "subtasks": [],
+        "dependencies": [],
+        "createdAt": "2026-04-25T12:30:00Z"
+      },
       {
         "id": 5,
         "title": "feat(kb): drag-to-resize splitter (both ask + search)",