Implement CE-WP-0005 T01-T08: demo app — sessions, uploads, ZIP archive

Turn the MVP into a self-contained demo. Users now:
  1. Land on an empty-state and create a named session.
  2. Drag-drop or pick arbitrary PDFs into that session.
  3. Annotate, build evidence, link to form fields — all session-scoped.
  4. Export the whole session as a single .zip archive (manifest +
     per-document PDFs).
  5. Import a .zip back — into a new session, or merged into an
     existing one (documents deduped by SHA-256 fingerprint;
     annotations/evidence/links added additively).

Architecture:
- New shared types: SessionId, Session, SessionArchiveManifest +
  parseSessionArchiveManifest with schema-version validation.
- SessionService (engine/services/sessions.ts) handles lifecycle
  (create/rename/delete/setActive) + emits 4 new events through its
  own bus; SharedContracts.md §4 lists the additions.
- SessionProvider (work/SessionContext.tsx) owns the cross-session
  state: service, per-session PdfByteStore registry, per-session
  version counter that drives EngineProvider remounts after imports.
- EngineProvider becomes session-aware (sessionId prop drives per-
  session localStorage keys). Bumping engineRevision after
  restoreFromStorage forces consumers to re-render so restored repos
  show up immediately.
- PdfByteStore (source/pdf/byte-store.ts) holds Uint8Array bytes per
  document and mints blob URLs; ingestPdfFromFile is the upload
  entry-point that wraps the existing ingestPdf pipeline.
- ADR-0008 locks the ZIP layout (manifest.json + documents/<id>.pdf),
  the manifest schema (schemaVersion 1), and the merge-on-collision
  policy. JSZip is the only new dependency.
- App.tsx restructured: SessionProvider at the root, EngineProvider
  keyed by ${sessionId}:${version}, hash routing #/s/<id>[/forms/demo],
  SessionMenu top-bar, CreateFirstSession empty state.
- New DocumentRemoved event for per-document delete cleanup in
  CollectionList; engine.documents.remove() is the new service method.

Tests:
- Unit: 16 SessionService lifecycle + persistence tests;
  per-session snapshot round-trip; PdfByteStore + ingestPdfFromFile;
  SessionArchive parser; exportSessionZip + importSessionZip with
  create + merge + corrupt-archive paths.
- DOM: UploadDropzone, session-scoped CollectionList delete,
  SessionMenu create/switch/rename, routing parser.
- E2E: tests/integration/session-export-reimport.dom.test.tsx walks
  the full create → annotate → export → reimport flow and asserts
  the additive merge (deduped doc + doubled evidence rows).
- Legacy E2Es updated to use a seed-session helper instead of the
  removed fixture-button flow.

Known limitation (documented in ADR-0008): re-importing your own
freshly-exported ZIP creates duplicate annotations. Forward pointer
left for an importBundleId follow-up.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/app/sessions/routing.ts

@@ -0,0 +1,61 @@
+/**
+ * Hash routing for the demo app.
+ *
+ *   #/                            → empty state ("create your first session")
+ *   #/s/<sessionId>               → review mode, scoped to <sessionId>
+ *   #/s/<sessionId>/forms/demo    → forms mode, scoped to <sessionId>
+ *
+ * The hash is the single source of truth for the active session and the
+ * active mode. `SessionProvider.setActive(...)` is wired as a side
+ * effect of hash changes so back/forward and deep links behave
+ * naturally.
+ */
+
+import type { SessionId } from "@shared/ids";
+
+export type AppMode = "review" | "forms";
+
+export interface AppRoute {
+  readonly sessionId: SessionId | null;
+  readonly mode: AppMode;
+}
+
+export const EMPTY_ROUTE: AppRoute = { sessionId: null, mode: "review" };
+
+export function parseRoute(hash: string): AppRoute {
+  // Normalise: drop leading "#", trim any trailing slashes.
+  const cleaned = hash.replace(/^#/, "").replace(/^\/+|\/+$/g, "");
+  if (cleaned === "") return EMPTY_ROUTE;
+  const parts = cleaned.split("/");
+  if (parts.length >= 2 && parts[0] === "s") {
+    const sessionId = parts[1]! as SessionId;
+    const mode: AppMode =
+      parts[2] === "forms" && parts[3] === "demo" ? "forms" : "review";
+    return { sessionId, mode };
+  }
+  // Legacy `#/forms/demo` (pre-CE-WP-0005) maps to the empty state — the
+  // user has to pick a session first.
+  return EMPTY_ROUTE;
+}
+
+export function serializeRoute(route: AppRoute): string {
+  if (!route.sessionId) return "";
+  const base = `#/s/${route.sessionId}`;
+  return route.mode === "forms" ? `${base}/forms/demo` : base;
+}
+
+export function navigateTo(route: AppRoute): void {
+  if (typeof window === "undefined") return;
+  const target = serializeRoute(route);
+  if (target === "") {
+    // Clear the hash entirely so the URL stays clean.
+    history.replaceState(null, "", window.location.pathname + window.location.search);
+    // history.replaceState doesn't fire hashchange — dispatch one so
+    // subscribers re-read.
+    window.dispatchEvent(new HashChangeEvent("hashchange"));
+    return;
+  }
+  if (window.location.hash !== target) {
+    window.location.hash = target;
+  }
+}