feat(blog): add markdown blog sourced from a gitea repo

posts are markdown files with yaml frontmatter (title, slug, date;
optional draft/public) in the grenade/blog repo. the worker's new
BlogSource polls the repo — one branch-tip request when nothing
changed — and upserts posts into events with source='blog' and
occurred_at from the frontmatter date, so imported posts keep their
original publish dates and backfill the contribution graph.

- new /v1/blog and /v1/blog/{slug} endpoints over the existing
  EventReader port; drafts stay hidden via the public gate
- new /blog and /blog/:slug routes, nav link, activity-feed entry
  with post icon and filter toggle; relative image srcs resolve to
  gitea raw urls
- shared Markdown component extracted from ProjectPage
- vite proxy target overridable via API_PROXY_TARGET for local dev

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/moments-entities/src/lib.rs

@@ -8,6 +8,7 @@ pub enum Source {
     Gitea,
     Hg,
     Bugzilla,
+    Blog,
 }
 
 impl Source {
@@ -16,6 +17,7 @@ impl Source {
         Source::Gitea,
         Source::Hg,
         Source::Bugzilla,
+        Source::Blog,
     ];
 
     pub fn as_str(&self) -> &'static str {
@@ -24,6 +26,7 @@ impl Source {
             Source::Gitea => "gitea",
             Source::Hg => "hg",
             Source::Bugzilla => "bugzilla",
+            Source::Blog => "blog",
         }
     }
 }
@@ -37,6 +40,7 @@ impl std::str::FromStr for Source {
             "gitea" => Ok(Source::Gitea),
             "hg" => Ok(Source::Hg),
             "bugzilla" => Ok(Source::Bugzilla),
+            "blog" => Ok(Source::Blog),
             other => Err(ParseSourceError(other.to_string())),
         }
     }
@@ -204,5 +208,28 @@ pub enum TimelineIcon {
     Star,
     Release,
     Bug,
+    Post,
     Generic,
 }
+
+/// Blog index entry returned by `GET /v1/blog`.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct BlogPostSummary {
+    pub slug: String,
+    pub title: String,
+    pub published_at: DateTime<Utc>,
+    pub excerpt: String,
+}
+
+/// Full blog post returned by `GET /v1/blog/{slug}`. The host/repo/branch
+/// triple lets the UI resolve relative image srcs to forge raw URLs.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct BlogPost {
+    pub slug: String,
+    pub title: String,
+    pub published_at: DateTime<Utc>,
+    pub markdown: String,
+    pub host: String,
+    pub repo: String,
+    pub branch: String,
+}