§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/PRView.jsx

@@ -23,11 +23,13 @@ import {
   withdrawPR,
 } from '../api'
 import { EVENTS, track } from '../lib/analytics'
+import { entryPath, entryPrPath, useProjectId } from '../lib/entryPaths'
 import LinkedText from './LinkedText'
 
 export default function PRView({ viewer }) {
   const { slug, prNumber: prNumberParam } = useParams()
   const navigate = useNavigate()
+  const pid = useProjectId()
   const prNumber = Number(prNumberParam)
 
   const [pr, setPR] = useState(null)
@@ -101,13 +103,13 @@ export default function PRView({ viewer }) {
     setError(null)
     try {
       const { resolution_branch } = await startResolutionBranch(slug, prNumber)
-      navigate(`/rfc/${slug}?branch=${encodeURIComponent(resolution_branch)}`)
+      navigate(`${entryPath(pid, slug)}?branch=${encodeURIComponent(resolution_branch)}`)
     } catch (e) {
       setError(e.message)
     } finally {
       setActing(null)
     }
-  }, [slug, prNumber, navigate])
+  }, [slug, prNumber, navigate, pid])
 
   const startHeaderEdit = useCallback(() => {
     setDraftTitle(pr?.title || '')
@@ -188,9 +190,9 @@ export default function PRView({ viewer }) {
       <div className="pr-header">
         <div className="pr-header-left">
           <div className="pr-breadcrumb">
-            <a href={`/rfc/${slug}`}>{pr.rfc_id || pr.slug}</a>
+            <a href={entryPath(pid, slug)}>{pr.rfc_id || pr.slug}</a>
             <span className="breadcrumb-sep">›</span>
-            <a href={`/rfc/${slug}?branch=${encodeURIComponent(pr.head_branch)}`}>{pr.head_branch}</a>
+            <a href={`${entryPath(pid, slug)}?branch=${encodeURIComponent(pr.head_branch)}`}>{pr.head_branch}</a>
             <span className="breadcrumb-sep">›</span>
             <strong>PR #{pr.pr_number}</strong>
           </div>
@@ -244,8 +246,8 @@ export default function PRView({ viewer }) {
           <StateBanner state={pr.state} mergedAt={pr.merged_at} closedAt={pr.closed_at} />
           {(supersedes || supersededBy) && (
             <div className="pr-supersedes">
-              {supersedes && <>Supersedes <a href={`/rfc/${slug}/pr/${supersedes}`}>#{supersedes}</a></>}
-              {supersededBy && <>Closed by <a href={`/rfc/${slug}/pr/${supersededBy}`}>#{supersededBy}</a></>}
+              {supersedes && <>Supersedes <a href={entryPrPath(pid, slug, supersedes)}>#{supersedes}</a></>}
+              {supersededBy && <>Closed by <a href={entryPrPath(pid, slug, supersededBy)}>#{supersededBy}</a></>}
             </div>
           )}
           <div className="pr-counts">