feat: add auto-update checker

Implements issue #17 - the app now checks for updates on startup and shows
a notification when a newer version is available. Users can disable this
in settings. Uses Gitea releases API with semver comparison.

Closes #17

src-tauri/src/commands.rs

@@ -1,5 +1,6 @@
 use tauri::{AppHandle, State};
 use tauri_plugin_store::StoreExt;
+use tauri_plugin_http::reqwest;
 
 use crate::config::{ClaudeStartOptions, HikariConfig};
 use crate::stats::UsageStats;
@@ -222,3 +223,74 @@ pub async fn list_skills() -> Result<Vec<String>, String> {
 
     Ok(skills)
 }
+
+#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
+pub struct UpdateInfo {
+    pub current_version: String,
+    pub latest_version: String,
+    pub has_update: bool,
+    pub release_url: String,
+    pub release_notes: Option<String>,
+}
+
+#[derive(Debug, serde::Deserialize)]
+struct GiteaRelease {
+    tag_name: String,
+    html_url: String,
+    body: Option<String>,
+    prerelease: bool,
+}
+
+#[tauri::command]
+pub async fn check_for_updates() -> Result<UpdateInfo, String> {
+    const CURRENT_VERSION: &str = env!("CARGO_PKG_VERSION");
+    const RELEASES_API: &str = "https://git.nhcarrigan.com/api/v1/repos/nhcarrigan/hikari-desktop/releases";
+
+    // Fetch releases from Gitea API
+    let client = reqwest::Client::new();
+    let response = client
+        .get(RELEASES_API)
+        .header("Accept", "application/json")
+        .send()
+        .await
+        .map_err(|e| format!("Failed to fetch releases: {}", e))?;
+
+    if !response.status().is_success() {
+        return Err(format!("API returned status: {}", response.status()));
+    }
+
+    let text = response
+        .text()
+        .await
+        .map_err(|e| format!("Failed to read response: {}", e))?;
+
+    let releases: Vec<GiteaRelease> = serde_json::from_str(&text)
+        .map_err(|e| format!("Failed to parse releases: {}", e))?;
+
+    // Find the latest non-prerelease, or fall back to latest prerelease
+    let latest = releases
+        .iter()
+        .find(|r| !r.prerelease)
+        .or_else(|| releases.first());
+
+    let latest = match latest {
+        Some(r) => r,
+        None => return Err("No releases found".to_string()),
+    };
+
+    // Parse version strings (remove 'v' prefix if present)
+    let current = semver::Version::parse(CURRENT_VERSION)
+        .map_err(|e| format!("Failed to parse current version: {}", e))?;
+
+    let latest_tag = latest.tag_name.trim_start_matches('v');
+    let latest_ver = semver::Version::parse(latest_tag)
+        .map_err(|e| format!("Failed to parse latest version: {}", e))?;
+
+    Ok(UpdateInfo {
+        current_version: CURRENT_VERSION.to_string(),
+        latest_version: latest.tag_name.clone(),
+        has_update: latest_ver > current,
+        release_url: latest.html_url.clone(),
+        release_notes: latest.body.clone(),
+    })
+}