feat: the front door answers "what arrived?" (milestone 387 step B1)

Moves FRONT_DOOR from /showcase to /latest. Showcase is a random
TABLESAMPLE — lean-back, and it can never tell you anything is wrong.
The feed is the only view where a failing source surfaces on its own,
as a creator who has gone quiet. The per-artist "new since last visit"
badges (#597) were a workaround for this view not being the door.

Showcase is demoted to a nav entry, not removed. Nothing is being
replaced, so rule 22's delete-the-legacy-path does not apply.

Deviation from the filed plan, deliberate: the step said write a new
LatestView.vue. Rejected — PostsView is ALREADY a self-contained feed
(own container, own store, infinite scroll, filters, deep-link
anchoring, empty state), and Browse only ever wrapped it in a tab
strip. A new view would have duplicated 231 working lines to gain
nothing. Mounting PostsView directly at its own route IS the whole
difference the promotion was after: a door you arrive at, not a hub
you navigate out of. Rule 28.

Backend untouched, as scoped — PostFeedService.scroll already does
cursor-paginated newest-first.

Two things this shook loose:

PostsView's deep-link "All posts" button was a hard `{ name: 'posts' }`,
which redirects into Browse. Correct while the view only ever rendered
inside Browse's tab; from the front door it would have yanked the
operator sideways into a different surface. Now returns to the current
route minus post_id, so Browse keeps its tab and any active scope.

The README claimed "A Showcase front page". That block is the SOURCE
the release notes quote (scripts/release_notes.py product_overview),
not a generated copy, so it is fixed here — a document contradicting
the code is the characteristic defect of the public-surface area.

No stickyChrome on the route: unlike Browse/Gallery/Settings this view
has no sticky sub-header for the nav to butt against.

The router spec pinned FRONT_DOOR to /showcase and now pins /latest,
plus that Showcase stayed reachable and in the nav — the demotion is
asserted, not assumed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LNXXULQDjVZmbuNa2G9mD9

frontend/src/router.js

@@ -9,15 +9,34 @@ import SeriesView from './views/SeriesView.vue'
 import SeriesManageView from './views/SeriesManageView.vue'
 import SeriesReaderView from './views/SeriesReaderView.vue'
 import SubscriptionsView from './views/SubscriptionsView.vue'
+import PostsView from './views/PostsView.vue'
 
 // The application's front door. `/` redirects here. Changing the front door
 // is a one-line edit (e.g. '/gallery' or '/tags').
-export const FRONT_DOOR = '/showcase'
+//
+// Moved from '/showcase' to '/latest' (milestone #387 B1). Showcase answers
+// "show me something" — a random TABLESAMPLE, lean-back, and it can never tell
+// you anything is wrong. The feed answers "what arrived?", which is a question
+// the operator has every day, and it is the only view where a failing source
+// shows up on its own as a creator who has gone quiet. The per-artist "new
+// since last visit" badges (#597) were a workaround for this view not being
+// the door. Showcase is demoted to a nav entry, not removed.
+export const FRONT_DOOR = '/latest'
 
 const routes = [
   // Root is a redirect only — no meta.title so it stays out of the nav.
   { path: '/', redirect: FRONT_DOOR },
 
+  // The front door (#387 B1): the post feed as its own surface. Reuses
+  // PostsView unchanged — it is already a self-contained feed (own container,
+  // own store, infinite scroll, deep-link anchoring), and Browse only ever
+  // wrapped it in a tab strip. Mounting it directly IS the difference the
+  // promotion was after: a door you arrive at, not a hub you navigate out of.
+  //
+  // No stickyChrome: unlike Browse/Gallery/Settings this view has no sticky
+  // sub-header for the nav to butt against, so the nav keeps its normal fade.
+  { path: '/latest', name: 'latest', component: PostsView, meta: { title: 'Latest', navOrder: 5 } },
+
   // FC-2: image backbone
   { path: '/showcase', name: 'showcase', component: ShowcaseView, meta: { title: 'Showcase', navOrder: 10 } },
   { path: '/gallery',  name: 'gallery',  component: GalleryView,  meta: { title: 'Gallery', navOrder: 20, stickyChrome: true } },