Precedent attachment UI in the compose screen

Surface the new POST/GET/DELETE /api/cases/{n}/precedents endpoints
in the compose screen as two insertion points:

1. A new case-level card "פסיקה כללית לדיון" at the top of the
   main column, for precedents that support the discussion intro
   rather than a specific threshold_claim / issue.
2. An inline "פסיקה תומכת" section inside each SubsectionCard,
   below the ChairEditor.

Both insertion points render a `<PrecedentsSection>` which shows a
list of `<PrecedentCard>` (citation + blockquote + optional chair
note + 📄 chip if a PDF was archived) followed by a `<PrecedentAttacher>`
popover trigger.

The Attacher is a Popover with cross-case typeahead: typing 2+
characters into the citation field hits /api/precedents/search and
shows distinct library matches; picking one prefills quote + chair
note but leaves them editable so customizing the quote for this
case doesn't mutate the library. An optional PDF/DOCX/DOC file can
be attached — it uploads first via POST .../upload-pdf and the
returned document_id is passed into the precedent create call.

The parent compose page issues a single useCasePrecedents query
and partitions the result by section_id into a Map so each
SubsectionCard renders its own slice without re-fetching.

shadcn Popover installed as a new primitive. sonner toasts wired
for success/error in both attach and delete flows.

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

.taskmaster/tasks/tasks.json

@@ -896,12 +896,24 @@
         "priority": "high",
         "subtasks": [],
         "updatedAt": "2026-04-11T17:15:57.831Z"
+      },
+      {
+        "id": "91",
+        "title": "Precedent attachment in compose screen",
+        "description": "Add case_precedents table + FastAPI endpoints + MCP tools + Next.js compose UI for attaching legal precedents (quote + citation + optional archived PDF) to threshold_claims/issues and to the case as a whole. Plan: ~/.claude/plans/woolly-cooking-graham.md",
+        "details": "",
+        "testStrategy": "",
+        "status": "in-progress",
+        "dependencies": [],
+        "priority": "high",
+        "subtasks": [],
+        "updatedAt": "2026-04-11T19:13:41.219Z"
       }
     ],
     "metadata": {
       "version": "1.0.0",
-      "lastModified": "2026-04-11T17:44:08.337Z",
-      "taskCount": 59,
+      "lastModified": "2026-04-11T19:13:41.220Z",
+      "taskCount": 60,
       "completedCount": 56,
       "tags": [
         "master"