feat: phase 1 public site skeleton — layout, routes, CSS, logo pipeline

Ship base Jinja layout (header/nav/main/footer with skip link and aria-current),
mobile-first single-file CSS using the ROADMAP palette tokens, and four public
routes: /, /about, /contact, /shop. Blog index renders via a stable
PostService.list_published() stub returning [] — Phase 2 only swaps the body.
About is static placeholder copy, /contact ships an inert form plus a mailto:
link driven by ADMIN_CONTACT_EMAIL, /shop shows a "Coming soon" card.

Adds a Pillow-based scripts/generate_static_assets.py producing resized logo
PNG + WebP, multi-size favicon.ico, and a 180x180 apple-touch-icon on a cream
background. Outputs committed for a reproducible build.

Also ship docs/MANUAL_TESTING.md with per-route / responsive / a11y / static-
asset checklists, and mark Phase 1 complete in docs/ROADMAP.md.

app/templates/public/partials/_post_card.html

@@ -0,0 +1,26 @@
+{#
+  Single blog card. Rendered once per PostSummary in the home-page loop.
+
+  Expects the loop variable `post` in scope with:
+    - post.slug          (str)
+    - post.title         (str)
+    - post.published_at  (datetime)
+    - post.excerpt       (str)
+
+  The post detail page does not exist yet (Phase 2 adds it), but we link
+  to /posts/<slug> anyway so the card markup is final. Phase 2 will
+  register the route; until then the link 404s, which is acceptable
+  because the post list itself is empty in Phase 1.
+#}
+<article class="post-card">
+  <header class="post-card__header">
+    <h2 class="post-card__title">
+      <a href="/posts/{{ post.slug }}">{{ post.title }}</a>
+    </h2>
+    <time class="post-card__date"
+          datetime="{{ post.published_at.isoformat() }}">
+      {{ post.published_at.strftime("%B %-d, %Y") }}
+    </time>
+  </header>
+  <p class="post-card__excerpt">{{ post.excerpt }}</p>
+</article>