feat: git status bar — show last commit link, remove branch name (#92)

* feat: show last commit hash in status bar, remove branch name

Replace the hardcoded "main" branch display with a clickable short SHA
linking to the GitHub commit. Add Rust get_last_commit_info command that
returns the last commit hash and constructs a GitHub URL from the remote.

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

* docs: add design/git-status-bar.pen with new status bar layout

Shows the updated status bar with commit hash link, no branch name,
and annotated change callouts.

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

* ci: retrigger — runner 3 pnpm not found (env issue)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -11,7 +11,7 @@ use std::path::Path;
 
 use ai_chat::{AiChatRequest, AiChatResponse};
 use frontmatter::FrontmatterValue;
-use git::{GitCommit, GitPullResult, ModifiedFile};
+use git::{GitCommit, GitPullResult, LastCommitInfo, ModifiedFile};
 use github::{DeviceFlowPollResult, DeviceFlowStart, GitHubUser, GithubRepo};
 use search::SearchResponse;
 use settings::Settings;
@@ -75,6 +75,11 @@ fn git_commit(vault_path: String, message: String) -> Result<String, String> {
     git::git_commit(&vault_path, &message)
 }
 
+#[tauri::command]
+fn get_last_commit_info(vault_path: String) -> Result<Option<LastCommitInfo>, String> {
+    git::get_last_commit_info(&vault_path)
+}
+
 #[tauri::command]
 fn git_pull(vault_path: String) -> Result<GitPullResult, String> {
     git::git_pull(&vault_path)
@@ -251,6 +256,7 @@ pub fn run() {
             get_file_diff,
             get_file_diff_at_commit,
             git_commit,
+            get_last_commit_info,
             git_pull,
             git_push,
             ai_chat,