§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/components/AcceptInvitation.jsx

@@ -23,10 +23,12 @@ import { useEffect, useState } from 'react'
 import { Link, useNavigate, useSearchParams } from 'react-router-dom'
 import { acceptInvitation, previewInvitation } from '../api'
 import { EVENTS, identify, track } from '../lib/analytics'
+import { entryPath, useProjectId } from '../lib/entryPaths'
 
 export default function AcceptInvitation({ viewer }) {
   const [searchParams] = useSearchParams()
   const navigate = useNavigate()
+  const pid = useProjectId()
   const token = searchParams.get('token') || ''
 
   const [preview, setPreview] = useState(null)
@@ -75,7 +77,7 @@ export default function AcceptInvitation({ viewer }) {
         rfc_slug: result.rfc_slug,
         role_in_rfc: result.role_in_rfc || preview?.role_in_rfc,
       })
-      navigate(`/rfc/${result.rfc_slug}`)
+      navigate(entryPath(pid, result.rfc_slug))
     } catch (err) {
       setAcceptError(err.message || 'Could not accept invitation.')
     } finally {
@@ -134,7 +136,7 @@ export default function AcceptInvitation({ viewer }) {
           The owner of <strong>{rfc_title}</strong> revoked this invitation.
           Ask them to re-issue it if you should still have access.
         </p>
-        <p><Link to={`/rfc/${rfc_slug}`}>Read the RFC anyway</Link></p>
+        <p><Link to={entryPath(pid, rfc_slug)}>Read the RFC anyway</Link></p>
       </div>
     )
   }
@@ -146,7 +148,7 @@ export default function AcceptInvitation({ viewer }) {
           This invitation to <strong>{rfc_title}</strong> has expired. Ask
           the RFC's owner to issue a fresh one.
         </p>
-        <p><Link to={`/rfc/${rfc_slug}`}>Read the RFC anyway</Link></p>
+        <p><Link to={entryPath(pid, rfc_slug)}>Read the RFC anyway</Link></p>
       </div>
     )
   }
@@ -156,7 +158,7 @@ export default function AcceptInvitation({ viewer }) {
         <h1>Already accepted</h1>
         <p>
           You've already accepted this invitation. You can{' '}
-          <Link to={`/rfc/${rfc_slug}`}>open {rfc_title}</Link> now.
+          <Link to={entryPath(pid, rfc_slug)}>open {rfc_title}</Link> now.
         </p>
       </div>
     )
@@ -200,7 +202,7 @@ export default function AcceptInvitation({ viewer }) {
         </button>
       </p>
       <p>
-        <Link to={`/rfc/${rfc_slug}`}>or just read the RFC without accepting</Link>
+        <Link to={entryPath(pid, rfc_slug)}>or just read the RFC without accepting</Link>
       </p>
     </div>
   )