feat(case-ui): merge /compose editor into case tabs (X17 #3)

Folds the standalone /compose decision-editor route into the main case page so
there is no more "sub-page" (mockup 18f), with the final 6-tab workflow order:
סקירה · טיעונים ועמדות · אימות פסיקה · ההחלטה · טיוטות והערות · סוכנים.

- New PositionsPanel — the chair's editing surface (threshold claims + issues
  SubsectionCards + ChairEditor + background prose + case precedents + finish
  rail), extracted verbatim from the former /compose "עמדות וטענות" tab. Drops
  only the doc-strip (the overview DocumentsPanel is the sole owner — no dup).
- "טיעונים ועמדות" tab = PositionsPanel above + the aggregated by-party
  LegalArgumentsPanel in a collapsible below.
- "אימות פסיקה" promoted to its own top-level tab (CitationVerificationPanel,
  was /compose tab 3); placed BEFORE "ההחלטה" — verify citations, then write
  (INV-AH: the writer cites only verified precedents).
- "ההחלטה" stays the single 12-block editor (DecisionBlocksPanel) — no longer
  duplicated between /compose and the case page.
- Tabs are now controlled; the "פתח עורך החלטה" CTA switches to the ההחלטה tab
  instead of navigating to the deleted route.
- /compose route deleted; header-context /compose special-case removed.

No duplication remains (G2): blocks editor single, docs single (overview),
citation-verify single. Design-gate: mockup 18f approved in Claude Design X17.
tsc --noEmit + eslint clean.

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

web-ui/src/components/header-context.ts

@@ -3,9 +3,8 @@
  * header. Reflects the current section so the user always sees where they
  * are without scanning the nav row.
  *
- * Special-cases case routes (`/cases/{caseNumber}` and `/compose`) so the
- * subtitle includes the case number — the most useful piece of context
- * during decision drafting.
+ * Special-cases case routes (`/cases/{caseNumber}`) so the subtitle includes
+ * the case number — the most useful piece of context during decision drafting.
  */
 export function headerSubtitle(pathname: string): string {
   if (pathname === "/") return "בית";
@@ -13,9 +12,8 @@ export function headerSubtitle(pathname: string): string {
   if (pathname.startsWith("/cases/")) {
     const [, , slug] = pathname.split("/");
     if (!slug || slug === "new") return "תיק חדש";
-    const isCompose = pathname.includes("/compose");
     const decoded = decodeURIComponent(slug);
-    return isCompose ? `ערר ${decoded} · ניסוח` : `ערר ${decoded}`;
+    return `ערר ${decoded}`;
   }
 
   if (pathname.startsWith("/archive"))     return "ארכיון";