Replace Strapi CMS with PocketBase

Strapi + Postgres are gone in favor of PocketBase: a single Go binary
with embedded SQLite, built-in admin UI and per-collection API rules.
No content existed yet, so this is a clean swap with no data migration.

Collections and rules are defined as code in pocketbase/pb_migrations/
and applied automatically on first boot. Draft & Publish has no native
PocketBase equivalent, so it's reproduced with a nullable `publishedAt`
field enforced by listRule/viewRule, matching the old Strapi semantics.

Routing flips: PocketBase's admin UI and REST/file API are hardwired to
`/_/` and `/api/*` at the domain root (its own dashboard assets and API
calls reference those paths directly, so a stripped path prefix like
`/admin/*` would break them). `/api` is therefore reserved for
PocketBase now, and the frontend's Nitro endpoints move to `/content/*`
(frontend/server/routes/content/, not server/api/). A `/admin` vanity
route in Nitro (not Caddy) redirects to `/_/`, so it works the same in
dev, where Caddy isn't part of the stack, and in production.

frontend/server/utils/strapi.ts becomes pocketbase.ts; queries.ts is
rewritten for PocketBase's filter/sort/fields/expand query syntax.
StrapiImage becomes MediaImage (no width/height — PocketBase file
fields don't store dimensions, and the cover images already reserve
their aspect ratio via CSS, so this is not a regression).

docs/*.md, CLAUDE.md and README.md are updated in the same commit.

frontend/nuxt.config.ts

@@ -20,18 +20,17 @@ export default defineNuxtConfig({
   },
 
   runtimeConfig: {
-    // Server-only: internal Strapi address, never exposed to the browser.
-    strapiUrl: 'http://localhost:1337',
-    strapiToken: '',
+    // Server-only: internal PocketBase address, never exposed to the browser.
+    pocketbaseUrl: 'http://localhost:8090',
     public: {
       // Canonical origin of the public website.
       siteUrl: 'http://localhost:3000',
-      // Browser-reachable Strapi origin, used to build absolute media URLs.
-      strapiUrl: 'http://localhost:1337',
+      // Browser-reachable PocketBase origin, used to build absolute media URLs.
+      pocketbaseUrl: 'http://localhost:8090',
     },
   },
 
   typescript: {
     strict: true,
   },
-})
+})