§22 M3 frontend: /p/<project>/ routing, runtime branding, directory, 308s (v0.35.0)

Implements the M3-frontend slice of the §22 multi-project track, per
docs/superpowers/specs/2026-06-03-m3-frontend-design.md (design merged in
#10). Completes the runtime-config cut 0.33.0 (M3-backend Plan A) began.

Frontend:
- DeploymentProvider boots GET /api/deployment → {name, tagline,
  defaultProjectId, projects}; brandTitle() neutral 'RFC' pre-fetch fallback.
- /p/:projectId/* routing with generic /e/<slug> segment. ProjectLayout
  fetches /api/projects/:id, applies per-project theme (reset on switch),
  provides ProjectContext, guards the corpus (served only for the default;
  others get NotServedPlaceholder — decouples this slice from Plan B).
- Directory at / (2+ projects) with N=1 redirect into the single project;
  ProjectSwitcher in deployment chrome; entry-noun by project type.
- VITE_APP_NAME hard cut: removed from vite.config + index.html; the 6 brand
  reads now use deployment.name via context; static <title>RFC</title> + JS
  document.title. Internal /rfc·/proposals links → /p/<project>/e|proposals
  via lib/entryPaths.

Backend:
- GET /api/deployment returns default_project_id (the guard contract).
- Server-side 308s: /rfc/<slug>, /rfc/<slug>/pr/<n>, /proposals/<n> →
  /p/<default>/… . nginx (testing + prod) routes /rfc/ and /proposals/ to
  the backend.

Tests: 3 new backend redirect/deployment tests (438 pass); Vitest unit for
DeploymentProvider, ProjectLayout (theme/guard/404), Directory (11 pass);
clean build with no VITE_APP_NAME. Playwright e2e deferred until Tier-1 seeds
a registry (see CHANGELOG 0.35.0 step 5).

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

frontend/src/lib/entryPaths.js

@@ -0,0 +1,32 @@
+// §22.10 — project-scoped path builders. After M3 every entry/proposal link
+// lives under `/p/<project>/…`. Until Plan B serves multiple corpora, that
+// project id is the deployment's corpus-served default for chrome surfaces, or
+// the contextual project when a component renders inside a project subtree
+// (ProjectContext). Components build links via these helpers so the later
+// per-project-serving slice flips them in one place.
+import { useProject } from '../components/ProjectLayout.jsx'
+import { useDeployment } from '../context/DeploymentProvider'
+
+export function entryPath(pid, slug) {
+  return `/p/${pid}/e/${slug}`
+}
+
+export function entryPrPath(pid, slug, prNumber) {
+  return `/p/${pid}/e/${slug}/pr/${prNumber}`
+}
+
+export function proposalPath(pid, prNumber) {
+  return `/p/${pid}/proposals/${prNumber}`
+}
+
+export function projectHome(pid) {
+  return `/p/${pid}/`
+}
+
+// The project id a component should build links against: the contextual
+// project when inside a `/p/:projectId/*` subtree, else the deployment default.
+export function useProjectId() {
+  const ctx = useProject()
+  const { defaultProjectId } = useDeployment()
+  return (ctx && ctx.projectId) || defaultProjectId
+}