feat(graph): halacha (rule) layer (corpus graph — closes Phase 2)

Enables the previously-disabled "הלכות" toggle. Each approved/published halacha
of a displayed precedent becomes a hal:<id> node linked to its parent
precedent (extracted_from); two cross-rule edges when both endpoints are in
view: corroborates (a later ruling cites the rule —
halacha_citation_corroboration) and equivalent (same principle from another
committee — equivalent_halachot). Node size = corroboration in-degree.

Backend (web/graph_api.py — read-only, G2):
- _halacha_nodes_and_edges(): halachot WHERE case_law_id in view AND
  review_status IN (approved, published), LIMIT 600; rule_type carried in the
  source_kind slot, rule_statement in note. Wired into both build functions
  (gated via node_types). Metrics still exclude halacha edges (only cites/
  precedent-typed feed PageRank). Validated: 185 halachot on the top-30
  precedents; 20 corroboration + 5 equivalent edges in the corpus.

Frontend:
- graph.ts: GraphEdgeType += extracted_from.
- graph-filter-panel: "הלכות" toggle enabled (was disabled "שלב ב׳").
- graph-canvas: amber halacha nodes; edge colours — extracted_from (faint
  amber), corroborates (amber), equivalent (violet).
- graph-node-panel: halacha branch — אזכורים + סוג כלל + rule text; "open in
  library" deep-links to the parent precedent.
- graph-view: halacha added to node + edge legends.

web-ui build + lint pass. Invariants: G2 (SELECT-only), UI2 (no model change —
reuses note/source_kind/case_law_id slots).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web-ui/src/components/graph/graph-node-panel.tsx

@@ -25,6 +25,14 @@ const TYPE_LABELS: Record<string, string> = {
   digest: "יומון",
 };
 
+const RULE_TYPE_LABELS: Record<string, string> = {
+  binding: "מחייב",
+  interpretive: "פרשני",
+  procedural: "דיוני",
+  obiter: "אמרת אגב",
+  application: "יישום",
+};
+
 const GAP_STATUS_LABELS: Record<string, string> = {
   open: "ממתינה לקליטה",
   uploaded: "הועלתה",
@@ -54,10 +62,12 @@ export function GraphNodePanel({
   onClose: () => void;
 }) {
   const isPrecedentLike = node.type === "precedent" || node.type === "halacha";
+  const isPrecedent = node.type === "precedent";
+  const isHalacha = node.type === "halacha";
   const isGap = node.type === "gap";
   const isDigest = node.type === "digest";
   // Rich detail (summary/headnote) for precedents — reuses the library hook.
-  const detailId = node.type === "precedent" ? node.case_law_id : null;
+  const detailId = isPrecedent ? node.case_law_id : null;
   const detail = usePrecedent(detailId);
   return (
     <Card className="bg-surface border-rule shadow-sm w-80 shrink-0 overflow-y-auto">
@@ -81,13 +91,25 @@ export function GraphNodePanel({
         </div>
 
         <dl className="space-y-2 text-sm">
-          {isPrecedentLike && (
-            <Row label="ציטוטים נכנסים" value={String(node.size)} />
+          {isPrecedent && <Row label="ציטוטים נכנסים" value={String(node.size)} />}
+          {isHalacha && (
+            <>
+              <Row label="אזכורים" value={String(node.size)} />
+              {node.source_kind && (
+                <Row
+                  label="סוג כלל"
+                  value={RULE_TYPE_LABELS[node.source_kind] ?? node.source_kind}
+                />
+              )}
+              {node.note && (
+                <p className="text-ink text-sm leading-relaxed m-0">{node.note}</p>
+              )}
+            </>
           )}
           {node.practice_area && (
             <Row label="תחום" value={PA_LABELS[node.practice_area] ?? node.practice_area} />
           )}
-          {node.source_kind && (
+          {isPrecedent && node.source_kind && (
             <Row label="מקור" value={SOURCE_LABELS[node.source_kind] ?? node.source_kind} />
           )}
           {node.precedent_level && <Row label="דרגה" value={node.precedent_level} />}