fix: restore status indicator symbol default

[abhishekvtangod]

Any reason why the default is dots? I'd prefer to keep symbols as the default.
They're more recognizable at a glance and make it easier to distinguish statuses quickly.

Summary

• revert the ui.status_indicators default and state/test expectations to symbols
• keep settings UI selection logic and sample config comments aligned
• update docs/config reference to show symbols as the default and explain opting into dots
• add abhishekvtangod to .github/APPROVED_CONTRIBUTORS so I can keep this PR updated

Testing

• env ZIG="/opt/homebrew/opt/zig@0.15/bin/zig" cargo test status_indicator
• env ZIG="/opt/homebrew/opt/zig@0.15/bin/zig" just test (fails: cross_area_agent_process_survives_detach_and_reattach panics when reattached frame lacks persisted working status)

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