Add a live switch to hide tab activity indicators

[WilliamWang1721]

Result / 用户结果

Add a default-on “Show tab activity indicators” switch under Appearance → Interface. Turning it off immediately hides activity and shell-status badges in sidebar/top tabs. Collapsed titles keep their existing identity display. Closes #139.

Design / 设计边界

The preference belongs to shared runtime settings, normal persistence and reset. Only the shared tab presentation changes: observations, Agent/Runtime state, command execution and background tasks remain active. Program identity, split counts and administrator safety indicators stay separate. The existing status/close slot and its hover, selection, keyboard and close handlers are preserved.

Evidence / 验证依据

Final head 2b6a693f477486d295bcbc9402e10b406f4748d2: architecture, lint, PR size and all required reports passed. Upstream validation executed Linux, Windows x64 and Windows ARM64. This is automated native-suite evidence; platform/device UI limits below still apply.

Two self-review passes completed. Regressions cover default/round-trip/reset, real switch clicks with persisted reload and hot application, sidebar/top status off/on, retained observed bell state, hover close controls, selection, Ctrl+Tab, actual close and collapsed title layout.

Final-head GitHub Actions validation passed; no local automated checks were run. Manual tmux/multi-device visual acceptance was not performed.

AI implementation/review: GPT-6.1 SOL sub-agents; coordinator model and reasoning efforts unverified.

Required Review / 必须确认

• Followed contributing, architecture, project constraints and typed i18n rules.
• Reused settings and presentation ownership; no task-state, observer or thread changes.
• Final-head formatting, architecture, selected native checks and every required context passed.
• Persistence and actual interaction coverage are included; existing tests and gates are preserved.