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/precedents-section.tsx

@@ -0,0 +1,50 @@
+"use client";
+
+import { PrecedentCard } from "@/components/compose/precedent-card";
+import { PrecedentAttacher } from "@/components/compose/precedent-attacher";
+import type { CasePrecedent } from "@/lib/api/precedents";
+import type { PracticeArea } from "@/lib/practice-area";
+
+/*
+ * Wrapper that renders the list of precedents for one scope — either
+ * case-level (sectionId=null) or a specific threshold_claim / issue.
+ * The parent page fetches useCasePrecedents(caseNumber) once and
+ * passes a pre-filtered slice down, so each section doesn't re-query.
+ */
+
+export function PrecedentsSection({
+  caseNumber,
+  sectionId,
+  precedents,
+  practiceArea,
+  emptyHelperText,
+}: {
+  caseNumber: string;
+  sectionId: string | null;
+  precedents: CasePrecedent[];
+  practiceArea: PracticeArea | null | undefined;
+  emptyHelperText?: string;
+}) {
+  return (
+    <div className="space-y-3">
+      {precedents.length === 0 ? (
+        emptyHelperText && (
+          <p className="text-[0.78rem] text-ink-muted">{emptyHelperText}</p>
+        )
+      ) : (
+        <ul className="space-y-2">
+          {precedents.map((p) => (
+            <li key={p.id}>
+              <PrecedentCard caseNumber={caseNumber} precedent={p} />
+            </li>
+          ))}
+        </ul>
+      )}
+      <PrecedentAttacher
+        caseNumber={caseNumber}
+        sectionId={sectionId}
+        practiceArea={practiceArea}
+      />
+    </div>
+  );
+}