fix: Gitea push 404 — add branch:main payload, handle 409 empty repo, clearer settings

- lib/git.ts: add branch:"main" to Gitea POST payload (required when repo has no
  branch yet or is freshly initialized); treat 409 on GET same as 404 (empty repo
  has no tree, Gitea returns 409 Conflict — proceed to create first file)
- lib/git.ts: improve 404 error hint with actionable checklist (URL format,
  owner/repo names, token scope, repo existence)
- settings.tsx: add Gitea info card clarifying URL format (no /api/v1), token
  format (raw value only, no "Bearer" prefix), repo initialization requirement

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/git.ts

@@ -71,7 +71,10 @@ async function pushGitea(
     if (existing.ok) {
       const data = await existing.json() as { sha?: string };
       sha = data.sha;
-    } else if (existing.status !== 404) {
+    } else if (existing.status === 404 || existing.status === 409) {
+      // 404 = file not found (normal for first push)
+      // 409 = repo is empty / no branch yet — proceed, we'll create with branch:"main"
+    } else {
       const body = await existing.text();
       return { success: false, error: `GET ${existing.status}: ${body.slice(0, 200)}` };
     }
@@ -79,6 +82,7 @@ async function pushGitea(
     const payload: Record<string, string> = {
       message: `incident: ${incident.title}`,
       content: base64Content,
+      branch: "main",
     };
     if (sha) payload.sha = sha;
 
@@ -94,7 +98,11 @@ async function pushGitea(
 
     if (!res.ok) {
       const body = await res.text();
-      return { success: false, error: `HTTP ${res.status}: ${body.slice(0, 300)}` };
+      let hint = "";
+      if (res.status === 404) {
+        hint = "\n\nCheck: instance URL (no /api/v1), owner and repo names are exact, token has write:repository scope, and the repo exists on Gitea.";
+      }
+      return { success: false, error: `HTTP ${res.status}: ${body.slice(0, 300)}${hint}` };
     }
     const data = await res.json() as { content?: { html_url?: string } };
     return { success: true, url: data.content?.html_url };