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/models/posts.py

@@ -0,0 +1,45 @@
+"""Blog post domain models.
+
+Phase 1 only needs the *list-view* projection of a post — a minimal
+immutable record sufficient to render a blog card on the home page.
+Phase 2 will introduce the richer persisted :class:`Post` dataclass that
+mirrors the SQLite schema; :class:`PostSummary` intentionally stays as a
+narrower DTO even after the DB arrives because list endpoints shouldn't
+pay the cost of loading full post bodies.
+
+The dataclass is frozen: summaries flow one-way from the service layer
+into templates and must never mutate mid-request.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from datetime import datetime
+
+
+@dataclass(frozen=True)
+class PostSummary:
+    """Immutable summary row for the blog index.
+
+    Attributes
+    ----------
+    slug:
+        URL-safe identifier used to build the post's canonical URL.
+    title:
+        Human-readable headline shown on the card.
+    published_at:
+        Timezone-aware UTC publish timestamp. Templates format this for
+        display; storing a real :class:`datetime` (rather than a
+        pre-formatted string) keeps locale/formatting concerns in the
+        view layer.
+    excerpt:
+        Short plaintext teaser. The service layer is responsible for
+        producing a sanitized, already-truncated excerpt so the template
+        can render it without additional escaping beyond Jinja's default
+        HTML autoescape.
+    """
+
+    slug: str
+    title: str
+    published_at: datetime
+    excerpt: str