fix: keep repeated launcher on existing bridge

[k9ight000]

Problem

Launching CodexPlusPlus a second time can acquire the existing-instance path, start a temporary helper, reinject the page, and then exit. The page is left pointing at the temporary helper, so conversation delete requests fail even though the delete controls remain visible.

Fix

• Keep the repeated-launcher path limited to activating the existing Codex window.
• Do not start another helper, reinject the renderer, or start another bridge watchdog.
• Add a regression assertion that the existing-instance path cannot recreate bridge components.

Validation

• cargo fmt --check --package codex-plus-launcher
• cargo test -p codex-plus-launcher --no-run
• cargo test -p codex-plus-core --test launcher -j 1 -- --skip app_paths_resolves_portable_current_link_to_directory_version — 74 passed

The skipped test requires Windows symbolic-link privilege and is unrelated to this change. The published diff contains only apps/codex-plus-launcher/src/main.rs and was scanned for credentials and local user paths.

[BigPizzaV3]

这个问题仍值得保留，但当前分支不能直接合并：最新 main 的重复启动路径已经承担 helper/注入恢复、远程会话修复和窗口激活等更多职责，旧补丁把 helper、ensure_injection 和 watchdog 整段移除，可能让“现有 bridge 已失效”的场景再也无法通过二次启动恢复。请基于最新 main 重做为“复用已健康 bridge；仅在健康检查失败时重建持久 bridge”，并补健康/失效两条回归测试后再评估。

[BigPizzaV3]

请基于当前 launcher/bridge 生命周期重做：健康 bridge 应复用，只有健康检查失败才重建持久 bridge，同时不能丢失 helper、注入恢复和 watchdog。请补健康/失效两条回归测试并跑三平台 CI。

[BigPizzaV3]

该 PR 的核心提交 acdf693d / f43d6468 已经在当前 main 的 launcher 生命周期修复中，功能已集成；分支当前也与 main 冲突，因此关闭此重复 PR。

[BigPizzaV3]

更正：刷新远端 main 后确认该修复尚未进入主线，已重新打开 PR。当前分支与 main 冲突，请 rebase 到最新 main，补跑三平台 CI，并验证重复启动不会创建第二个 helper/bridge。

[BigPizzaV3]

关闭理由：分支基于很旧的 main（11179a01），已与当前 main 冲突，且该作者同期的 #1777 一并关闭。若继续请基于最新 main rebase 后重开。