feat: about tab with update check/download (Gitea feed first, GitHub fallback)

- updater: dual-feed state machine, manual check/download/install IPC,
  changelog from Gitea releases API with GitHub fallback
- settings: new About tab (version, channel, auto-check toggle, progress)
- system.autoCheckUpdate setting gates the startup check

src/shared/api.ts

@@ -8,6 +8,7 @@ import type {
   SessionOpenResult
 } from './ipc'
 import type { AppSettings } from './settings'
+import type { ReleaseNote, UpdateState } from './ipc'
 import type {
   HostKeyAction,
   HostKeyPromptEvent,
@@ -105,4 +106,11 @@ export interface AppApi {
   /** json = serialized dockview layout (DockviewApi.toJSON()) */
   saveLayout(meta: LayoutMeta, json: string): Promise<void>
   deleteLayout(id: string): Promise<void>
+
+  // ---- updater (domestic feed first, GitHub fallback) ----
+  updateCheck(): Promise<UpdateState>
+  updateDownload(): Promise<void>
+  updateInstall(): void
+  updateChangelog(): Promise<ReleaseNote[]>
+  onUpdateState(cb: (s: UpdateState) => void): () => void
 }

src/shared/ipc.ts

@@ -90,7 +90,15 @@ export const Ipc = {
   ZMODEM_DONE: 'zmodem:done',
 
   // ---- misc ----
-  APP_INFO: 'app:info'
+  APP_INFO: 'app:info',
+
+  // ---- updater (check/download/install + state broadcast) ----
+  UPDATE_CHECK: 'update:check',
+  UPDATE_DOWNLOAD: 'update:download',
+  UPDATE_INSTALL: 'update:install',
+  UPDATE_CHANGELOG: 'update:changelog',
+  /** main -> renderer broadcast: UpdateState */
+  UPDATE_STATE: 'update:state'
 } as const
 
 export interface PtyCreateOptions {
@@ -122,6 +130,37 @@ export interface AppInfo {
   homeDir: string
 }
 
+// ---- updater ----
+export type UpdateStatus =
+  | 'idle'
+  | 'checking'
+  | 'available'
+  | 'latest'
+  | 'downloading'
+  | 'downloaded'
+  | 'error'
+  /** dev builds have no update channel */
+  | 'dev'
+
+export interface UpdateState {
+  status: UpdateStatus
+  /** running app version */
+  currentVersion: string
+  /** newer version when available/downloading/downloaded */
+  version?: string
+  /** 0-100 while downloading */
+  percent?: number
+  error?: string
+  /** which feed served the last check: domestic Gitea first, GitHub fallback */
+  feed?: 'gitea' | 'github'
+}
+
+export interface ReleaseNote {
+  version: string
+  date: string
+  body: string
+}
+
 export interface LayoutMeta {
   id: string
   name: string

src/shared/settings.ts

@@ -47,6 +47,8 @@ export interface SystemSettings {
   globalShowHide?: string
   /** close-button behavior: prompt every time / hide to tray / quit directly */
   closeAction?: 'ask' | 'tray' | 'exit'
+  /** check for updates shortly after startup (manual check always available) */
+  autoCheckUpdate?: boolean
 }
 
 export interface AppSettings {
@@ -102,5 +104,5 @@ export const DEFAULT_SETTINGS: AppSettings = {
   },
   customThemes: [],
   highlightRules: DEFAULT_HIGHLIGHT_RULES,
-  system: { launchAtLogin: false, preventSleep: false, globalShowHide: '', closeAction: 'ask' }
+  system: { launchAtLogin: false, preventSleep: false, globalShowHide: '', closeAction: 'ask', autoCheckUpdate: true }
 }