§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/ProposalView.jsx

@@ -12,6 +12,7 @@ import { useEffect, useState } from 'react'
 import { useParams, useNavigate } from 'react-router-dom'
 import { renderMarkdown } from '../lib/sanitizeHtml'
 import { getProposal, mergeProposal, declineProposal, withdrawProposal } from '../api'
+import { entryPath, useProjectId } from '../lib/entryPaths'
 
 export default function ProposalView({ viewer, onChange }) {
   const { prNumber } = useParams()
@@ -21,6 +22,7 @@ export default function ProposalView({ viewer, onChange }) {
   const [declineOpen, setDeclineOpen] = useState(false)
   const [declineComment, setDeclineComment] = useState('')
   const navigate = useNavigate()
+  const pid = useProjectId()
 
   function refresh() {
     setData(null); setError(null)
@@ -39,7 +41,7 @@ export default function ProposalView({ viewer, onChange }) {
     try {
       const { slug } = await mergeProposal(prNumber)
       onChange?.()
-      navigate(`/rfc/${slug}`)
+      navigate(entryPath(pid, slug))
     } catch (e) {
       setError(e.message)
       setActing(false)