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/app/pages/index.vue

@@ -1,7 +1,7 @@
 <script setup lang="ts">
 import type { ArticleSummary, Paginated } from '#shared/types/blog'
 
-const { data, error } = await useFetch<Paginated<ArticleSummary>>('/api/articles', {
+const { data, error } = await useFetch<Paginated<ArticleSummary>>('/content/articles', {
   key: 'home-articles',
   query: { page: 1 },
 })
@@ -82,9 +82,7 @@ useSeoMeta({
         >
           <img
             :src="featuredCover"
-            :alt="featured.cover?.alternativeText ?? ''"
-            :width="featured.cover?.width ?? undefined"
-            :height="featured.cover?.height ?? undefined"
+            :alt="featured.cover?.alt ?? ''"
           >
         </NuxtLink>