§22 M3-backend Plan B (2/2, read path): per-project RFC serving (v0.37.0)

A second project's corpus now renders under /p/<id>/, isolated by its own
slug namespace. Completes step (1) "RFC app supports multiple projects" for
the read path.

- api.py: GET /api/projects/{pid}/rfcs (scoped catalog) + /{slug} (entry by
  (project_id,slug)), behind the §22.5 read gate. Unscoped /api/rfcs stay as
  default-project compat.
- cache.py: refresh_meta_repo iterates every projects row, mirroring each
  content_repo into cached_rfcs stamped with its project_id (_upsert_cached_rfc
  gains a project_id arg).
- frontend: api.listRFCs(projectId)/getRFC(projectId,slug); Catalog + RFCView
  pass useProjectId(); ProjectLayout's NotServedPlaceholder guard removed (every
  project serves), 404/not-readable branch kept; NotServedPlaceholder deleted.
- tests: test_project_scoped_serving.py (catalog scoping, entry isolation,
  gated 404); ProjectLayout.test updated (non-default renders). 445 backend +
  11 Vitest green; clean build.

Known limitation (next slice): write path + default-id re-stamp not yet scoped
(non-default project read-only); no live impact (no 2nd project in prod yet).
Per docs/superpowers/specs/2026-06-04-m3-backend-planb-design.md.

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

frontend/src/components/ProjectLayout.jsx

@@ -16,8 +16,6 @@ import { createContext, useContext, useEffect, useState } from 'react'
 import { useParams } from 'react-router-dom'
 import { getProject } from '../api'
 import { brandTitle } from '../lib/brand'
-import { useDeployment } from '../context/DeploymentProvider'
-import NotServedPlaceholder from './NotServedPlaceholder.jsx'
 
 const ProjectContext = createContext(null)
 
@@ -42,7 +40,6 @@ const THEME_TOKENS = {
 
 export default function ProjectLayout({ children }) {
   const { projectId } = useParams()
-  const deployment = useDeployment()
   const [project, setProject] = useState(null)
   const [status, setStatus] = useState('loading') // loading | ready | notfound
 
@@ -90,10 +87,11 @@ export default function ProjectLayout({ children }) {
     )
   }
 
-  const served = projectId === deployment.defaultProjectId
+  // §22.4 (Plan B): every registry project now serves its own corpus, so
+  // there is no "not served" guard — a readable project renders its children.
   return (
-    <ProjectContext.Provider value={{ project, projectId, served, noun: entryNoun(project?.type) }}>
-      {served ? children : <NotServedPlaceholder project={project} />}
+    <ProjectContext.Provider value={{ project, projectId, noun: entryNoun(project?.type) }}>
+      {children}
     </ProjectContext.Provider>
   )
 }