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>

web-ui/src/components/compose/subsection-card.tsx

@@ -3,16 +3,23 @@
 import { useState } from "react";
 import { ChevronDown } from "lucide-react";
 import { ChairEditor } from "@/components/compose/chair-editor";
+import { PrecedentsSection } from "@/components/compose/precedents-section";
 import type { ResearchSubsection } from "@/lib/api/research";
+import type { CasePrecedent } from "@/lib/api/precedents";
+import type { PracticeArea } from "@/lib/practice-area";
 
 export function SubsectionCard({
   caseNumber,
   item,
   defaultOpen = false,
+  precedents = [],
+  practiceArea,
 }: {
   caseNumber: string;
   item: ResearchSubsection;
   defaultOpen?: boolean;
+  precedents?: CasePrecedent[];
+  practiceArea?: PracticeArea | null;
 }) {
   const [open, setOpen] = useState(defaultOpen);
   const isFilled = Boolean(item.chair_position?.trim());
@@ -81,6 +88,18 @@ export function SubsectionCard({
             sectionId={item.id}
             initialValue={item.chair_position ?? ""}
           />
+          <div className="border-t border-rule pt-4 mt-2">
+            <h4 className="text-[0.78rem] uppercase tracking-wider text-gold-deep font-semibold mb-2">
+              פסיקה תומכת
+            </h4>
+            <PrecedentsSection
+              caseNumber={caseNumber}
+              sectionId={item.id}
+              precedents={precedents}
+              practiceArea={practiceArea}
+              emptyHelperText="עדיין לא צורפה פסיקה לסעיף זה"
+            />
+          </div>
         </div>
       )}
     </article>