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/display-app.test.tsx

@@ -251,10 +251,13 @@ describe("display host — full-viewport boundary", () => {
       "contributions",
       "display",
       "moduleId",
+      "navigation",
       "permissions",
       "principal",
       "realtime",
     ]);
+    // A display is one screen with no pages: the display host offers no navigation (ADR 0063).
+    expect(seenContext?.navigation).toBeUndefined();
     expect(seenContext?.principal).toEqual({ kind: "authenticated", userId: "user-1" });
     expect(isolatedText(query("display-module-container"))).toBe("permitted");
     expect(
@@ -352,6 +355,7 @@ describe("display host — full-viewport boundary", () => {
                 version: "1.2.0",
               },
               name: "Announcements",
+              navigation: { icon: null, pages: [] },
             },
           ],
         });