Add personalization, outbound feeds, and PWA/push to the web UI

A multi-session build turning Pete's read-only web UI into something people
return to. Five phases, signed-in features keyed off the OIDC subject; anonymous
visitors keep the reverse-chron feed and localStorage-only state.

Phase 1 — per-user read + bookmark state: user_story_state table +
storage/userstate.go; auth-gated /api/read, /api/bookmark, /api/state and a
/bookmarks page; reader.js syncs state server-side for signed-in users. Also
hides the Matrix-posting UI when posting.enabled=false (web-only mode).

Phase 2 — outbound feeds: storage.ListForFeed + web/feed.go hand-build RSS 2.0
(content:encoded) and JSON Feed 1.1 (no new dep); /feed.xml, /feed.json and
per-channel variants; <link rel=alternate> discovery tags.

Phase 3 — "For you" + related: storage/rank.go scores recent unread candidates
by channel/source affinity + recency decay; RelatedStories via FTS5. ForYou rail
+ /for-you page; public /api/related feeds the reader's "You might also like".

Phase 4 — source-health dashboard: source_health table + storage/sourcehealth.go
(RecordPollResult, ListSourceHealth, SourceContentStats), written by the poller;
admin-gated /status page behind web.admin_subs.

Phase 5 — PWA + offline reader + Web Push: root-scoped manifest.webmanifest and
sw.js (app-shell precache, /api/article runtime cache for offline reading,
offline fallback, push/notificationclick handlers); PNG icons from pete.avif;
pwa.js registers the SW and drives a notifications toggle. Web Push adds
webpush-go, a [web.push] config block (pete -genvapid mints VAPID keys), a
push_subscriptions table, auth-gated subscribe/unsubscribe endpoints, and a
digest sender that pings each subscriber "N new stories" past their watermark,
honoring disabled-sources and pruning gone endpoints.

Tests added beside each new storage/web file; go test ./... and go vet clean.

internal/web/templates/_card.html

@@ -11,6 +11,13 @@
    data-posted="{{if .Story.Posted}}1{{end}}"
    data-paywalled="{{if .Story.Paywalled}}1{{end}}"
    class="group relative block rounded-3xl bg-[color:var(--card)] border-2 {{if .Story.Posted}}border-theme-{{.Theme}} glow-theme-{{.Theme}}{{else}}border-[color:var(--ink)]/10{{end}} shadow-pete overflow-hidden hover:-translate-y-1 hover:shadow-pete-lg transition">
+  <span role="button" tabindex="0" data-bookmark-btn data-story-id="{{.Story.ID}}"
+        aria-label="Bookmark this story" aria-pressed="false"
+        style="display:none;position:absolute;top:.6rem;left:.6rem;z-index:6;height:1.9rem;width:1.9rem;align-items:center;justify-content:center;border-radius:9999px;background:rgba(20,14,6,.62);color:#fff;-webkit-backdrop-filter:blur(2px);backdrop-filter:blur(2px)">
+    <svg viewBox="0 0 24 24" width="15" height="15" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+      <path d="M6 2h12a1 1 0 0 1 1 1v18l-7-4-7 4V3a1 1 0 0 1 1-1z"></path>
+    </svg>
+  </span>
   {{if .Story.ImageURL}}
   <div class="aspect-[16/10] w-full overflow-hidden bg-[color:var(--ink)]/5">
     <img src="{{thumb .Story.ImageURL}}" alt="" loading="lazy" decoding="async"