refactor: extract github.rs from git.rs, move tests to vault.rs

Completes the commands/ module split: GitHub commands now live in
github.rs (88 lines) instead of bloating git.rs (318→233). Vault
and frontmatter tests moved from mod.rs to vault.rs where they
belong (mod.rs 254→93 lines, CodeScene 9.24→9.84). Deduplicated
batch_archive/trash test setup with a shared temp_note helper.

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

src-tauri/src/commands/github.rs

@@ -0,0 +1,88 @@
+use crate::github::{DeviceFlowPollResult, DeviceFlowStart, GitHubUser, GithubRepo};
+
+use super::expand_tilde;
+
+// ── GitHub commands (desktop) ───────────────────────────────────────────────
+
+#[cfg(desktop)]
+#[tauri::command]
+pub async fn github_list_repos(token: String) -> Result<Vec<GithubRepo>, String> {
+    crate::github::github_list_repos(&token).await
+}
+
+#[cfg(desktop)]
+#[tauri::command]
+pub async fn github_create_repo(
+    token: String,
+    name: String,
+    private: bool,
+) -> Result<GithubRepo, String> {
+    crate::github::github_create_repo(&token, &name, private).await
+}
+
+#[cfg(desktop)]
+#[tauri::command]
+pub fn clone_repo(url: String, token: String, local_path: String) -> Result<String, String> {
+    let local_path = expand_tilde(&local_path);
+    crate::github::clone_repo(&url, &token, &local_path)
+}
+
+#[cfg(desktop)]
+#[tauri::command]
+pub async fn github_device_flow_start() -> Result<DeviceFlowStart, String> {
+    crate::github::github_device_flow_start().await
+}
+
+#[cfg(desktop)]
+#[tauri::command]
+pub async fn github_device_flow_poll(device_code: String) -> Result<DeviceFlowPollResult, String> {
+    crate::github::github_device_flow_poll(&device_code).await
+}
+
+#[cfg(desktop)]
+#[tauri::command]
+pub async fn github_get_user(token: String) -> Result<GitHubUser, String> {
+    crate::github::github_get_user(&token).await
+}
+
+// ── GitHub commands (mobile stubs) ──────────────────────────────────────────
+
+#[cfg(mobile)]
+#[tauri::command]
+pub async fn github_list_repos(_token: String) -> Result<Vec<GithubRepo>, String> {
+    Err("GitHub integration is not available on mobile".into())
+}
+
+#[cfg(mobile)]
+#[tauri::command]
+pub async fn github_create_repo(
+    _token: String,
+    _name: String,
+    _private: bool,
+) -> Result<GithubRepo, String> {
+    Err("GitHub integration is not available on mobile".into())
+}
+
+#[cfg(mobile)]
+#[tauri::command]
+pub fn clone_repo(_url: String, _token: String, _local_path: String) -> Result<String, String> {
+    Err("Git clone is not available on mobile".into())
+}
+
+#[cfg(mobile)]
+#[tauri::command]
+pub async fn github_device_flow_start() -> Result<DeviceFlowStart, String> {
+    Err("GitHub integration is not available on mobile".into())
+}
+
+#[cfg(mobile)]
+#[tauri::command]
+pub async fn github_device_flow_poll(_device_code: String) -> Result<DeviceFlowPollResult, String> {
+    Err("GitHub integration is not available on mobile".into())
+}
+
+#[cfg(mobile)]
+#[tauri::command]
+pub async fn github_get_user(_token: String) -> Result<GitHubUser, String> {
+    Err("GitHub integration is not available on mobile".into())
+}