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.

docker-compose.dev.yml

@@ -1,18 +1,14 @@
 # Local testing without domains or TLS: publishes the app ports on localhost and
 # leaves Caddy out. Never used in production — it must be passed explicitly:
-#   docker compose -f docker-compose.yml -f docker-compose.dev.yml up -d --build cms frontend
+#   docker compose -f docker-compose.yml -f docker-compose.dev.yml up -d --build pocketbase frontend
 services:
-  database:
+  pocketbase:
     ports:
-      - "127.0.0.1:5432:5432"
-
-  cms:
-    ports:
-      - "127.0.0.1:1337:1337"
+      - "127.0.0.1:8090:8090"
 
   frontend:
     ports:
       - "127.0.0.1:3000:3000"
     environment:
       NUXT_PUBLIC_SITE_URL: http://localhost:3000
-      NUXT_PUBLIC_STRAPI_URL: http://localhost:1337
+      NUXT_PUBLIC_POCKETBASE_URL: http://localhost:8090