fix: source-aware repo extraction, Gitea readme/languages endpoints

Use CASE/source instead of COALESCE for repo name extraction — Gitea's
repo.name is the short name while full_name includes the owner prefix.
Fix Gitea README fetch to use /contents/README.md with base64 decoding
instead of the nonexistent /readme endpoint.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/api/client.ts

@@ -102,20 +102,26 @@ export async function fetchProjects(): Promise<ProjectSummary[]> {
   return resp.json();
 }
 
-/** Fetch repo README as rendered HTML or raw markdown. */
+/** Fetch repo README as raw markdown. */
 export async function fetchReadme(source: Source, host: string, repo: string): Promise<string | null> {
-  const baseUrl = source === 'github'
-    ? `https://api.github.com/repos/${repo}/readme`
-    : source === 'gitea'
-      ? `https://${host}/api/v1/repos/${repo}/readme`
-      : null;
-  if (!baseUrl) return null;
-
-  const resp = await fetch(baseUrl, {
-    headers: { 'Accept': 'application/vnd.github.raw+json' },
-  });
-  if (!resp.ok) return null;
-  return resp.text();
+  if (source === 'github') {
+    const resp = await fetch(`https://api.github.com/repos/${repo}/readme`, {
+      headers: { 'Accept': 'application/vnd.github.raw+json' },
+    });
+    if (!resp.ok) return null;
+    return resp.text();
+  }
+  if (source === 'gitea') {
+    // Gitea returns JSON with base64-encoded content
+    const resp = await fetch(`https://${host}/api/v1/repos/${repo}/contents/README.md`);
+    if (!resp.ok) return null;
+    const data = await resp.json();
+    if (data.encoding === 'base64' && data.content) {
+      return atob(data.content);
+    }
+    return data.content ?? null;
+  }
+  return null;
 }
 
 /** Fetch repo languages as { language: bytes } map. */