fix: apply the review items for #714 at merge

- Session update no longer resets "How often" while typing: updateGitFetchStatus
  (session-ui.js) leaves a control alone while it is document.activeElement, and
  autoSaveGitFetch writes the clamped interval back itself (Enter saves with the
  field still focused).
- Partial override shows the app values: enabled = session ?? app switch,
  interval = session ?? app interval ?? 300 (session-ui.js updateGitFetchStatus).
- runFetch (git-fetch.ts) arms the spawn with what the core.sshCommand read left
  of timeoutMs, and answers ETIMEDOUT without spawning when nothing is left, so a
  git that never answers costs one timeout, not two.
- fetchEnvFor keeps a GIT_SSH from the server's environment (repoSshCommand ||
  base.GIT_SSH), fileoverview and CLAUDE.md line updated to say so.
- i18n.js: the zh-CN "Git fetch on an interval" description scopes the only
  writing git command to the Git window.
- styles.css: the disabled/busy rules are scoped to .git-status-actions
  .btn-icon-sm (moved beside .git-status-actions), and the busy pulse stops
  under prefers-reduced-motion.
- Comments that called the override per case now say per session: session.ts
  (field, restore and getter docs, setGitFetchSettings), git-fetch-scheduler.ts:2,
  server-timing.ts:78, server.ts (cleanup and restore), app.js _onSessionUpdated,
  session-ui.js (openSessionOptions and updateGitFetchStatus).
- Tests: test/git-fetch-session-options-ui.test.ts (new, JSDOM: typing survives
  an SSE update, the Enter write-back, both partial cases); test/git-fetch.test.ts
  (GIT_SSH kept; one bound for the read and the fetch, stub git on PATH).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/session.ts

@@ -615,9 +615,9 @@ export class Session extends EventEmitter {
   private _keepWarmEnabled: boolean | undefined;
   /** Last status the keep-warm service published for this session; ephemeral. */
   private _keepWarm: KeepWarmStatus | null = null;
-  /** Git fetch on an interval for this case; undefined = follow the app-wide default. Persisted. */
+  /** Git fetch on an interval for this session; undefined = follow the app-wide default. Persisted. */
   private _gitFetchEnabled: boolean | undefined;
-  /** Seconds between this case's fetch runs; undefined = follow the app-wide default. Persisted. */
+  /** Seconds between this session's fetch runs; undefined = follow the app-wide default. Persisted. */
   private _gitFetchIntervalSeconds: number | undefined;
   /** Last status the fetch scheduler published for this session; ephemeral. */
   private _gitFetch: GitFetchStatus | null = null;
@@ -933,9 +933,9 @@ export class Session extends EventEmitter {
       lastRealPromptAt?: number;
       /** Restored prompt-cache keep-warm choice (see `keepWarmEnabled`). */
       keepWarmEnabled?: boolean;
-      /** Restored Git fetch override for this case (see `gitFetchEnabled`). */
+      /** Restored Git fetch override for this session (see `gitFetchEnabled`). */
       gitFetchEnabled?: boolean;
-      /** Restored Git fetch interval for this case (see `gitFetchIntervalSeconds`). */
+      /** Restored Git fetch interval for this session (see `gitFetchIntervalSeconds`). */
       gitFetchIntervalSeconds?: number;
       /** Restored conversation chain, oldest first (see `claudeSessionChain`). */
       claudeSessionChain?: string[];
@@ -1594,18 +1594,18 @@ export class Session extends EventEmitter {
     return changed;
   }
 
-  /** Git fetch override for this case; undefined means the app-wide setting applies. */
+  /** Git fetch override for this session; undefined means the app-wide setting applies. */
   get gitFetchEnabled(): boolean | undefined {
     return this._gitFetchEnabled;
   }
 
-  /** Interval override for this case; undefined means the app-wide setting applies. */
+  /** Interval override for this session; undefined means the app-wide setting applies. */
   get gitFetchIntervalSeconds(): number | undefined {
     return this._gitFetchIntervalSeconds;
   }
 
   /**
-   * Set the case's override. The Session Options rows save on their own, so a caller passes what it has
+   * Set the session's override. The Session Options rows save on their own, so a caller passes what it has
    * and leaves the other half as it was; `undefined` on either means the app-wide setting applies again.
    */
   setGitFetchSettings(enabled: boolean | undefined, intervalSeconds: number | undefined): void {