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/static/manifest.webmanifest

@@ -0,0 +1,22 @@
+{
+  "name": "Pete — friendly news",
+  "short_name": "Pete",
+  "description": "A calm, read-one-at-a-time news reader. Bookmarks, a personalized feed, and offline reading.",
+  "id": "/",
+  "start_url": "/?source=pwa",
+  "scope": "/",
+  "display": "standalone",
+  "orientation": "portrait-primary",
+  "background_color": "#fbf3e3",
+  "theme_color": "#fbf3e3",
+  "categories": ["news", "productivity"],
+  "icons": [
+    { "src": "/static/img/icon-192.png", "sizes": "192x192", "type": "image/png", "purpose": "any" },
+    { "src": "/static/img/icon-512.png", "sizes": "512x512", "type": "image/png", "purpose": "any" },
+    { "src": "/static/img/maskable-512.png", "sizes": "512x512", "type": "image/png", "purpose": "maskable" }
+  ],
+  "shortcuts": [
+    { "name": "For you", "short_name": "For you", "url": "/for-you", "description": "Your personalized feed" },
+    { "name": "Bookmarks", "short_name": "Saved", "url": "/bookmarks", "description": "Stories you saved" }
+  ]
+}