Add the module navigation contract: manifest v9, module routes, return-to-origin

Stage 1 PR 7 (ADR 0063). A module becomes a first-class part of the Dashboard.

- Manifest v9 = v8 plus optional `navigation`: a Lucide icon from the curated
  MODULE_NAVIGATION_ICONS set, and up to 12 primary pages (stable id, safe
  label, kebab-case path relative to the module root; no traversal, schemes,
  queries, duplicates, or nesting). Validated before activation.
- Version 8 stays accepted beside version 9, each read strictly as itself
  (discriminated union); no released manifest is rewritten. The template
  moves to v9; the released Signage 0.1.5 manifest is a test fixture.
- Real module routes: /<id> is the landing view, /<id>/<page> a declared
  page, anything beneath a page a module-owned detail route; anything else
  is not-found and mounts nothing. api/assets/display are never pages.
- Sidebar: declared icons, pages nested under an open module, one
  aria-current, collapsed and drawer behaviour; v8 modules unchanged.
- module-ui-sdk: ModuleUiHostContext.navigation (location, subscribe,
  navigate, link, settings), refusing anything outside the module's routes;
  undefined on the display host. Mount ABI unchanged.
- Return-to-origin: one `?return=` carrier on Settings URLs, validated by
  parseReturnTarget and against running modules' declared routes; Settings
  Back returns to exactly the originating module page, across refreshes.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

surfaces/shell/tests/modularity.test.ts

@@ -179,7 +179,15 @@ describe("the shell builds no module knowledge into its bundle", () => {
     // mean the shell had an opinion about an arrangement it must only render.
     // Deliberately distinctive terms: a generic word like "media" appears inside React's own
     // bundled source and would make this assertion meaningless rather than strict.
-    for (const term of ["planning", "sunday-production", "livestream", "calendar", "ungrouped-"]) {
+    // "calendar" is no longer one of them: it is a generic Lucide icon a module may declare
+    // (ADR 0063), so the bundle names it on purpose.
+    for (const term of [
+      "planning",
+      "sunday-production",
+      "livestream",
+      "youth-ministry",
+      "ungrouped-",
+    ]) {
       expect(bundle.toLowerCase(), term).not.toContain(term);
     }
   });