Detects when 2+ agent sessions write the same file within a project.
New conflicts.svelte.ts store, shared tool-files.ts utility, dispatcher
integration, health attention scoring (SCORE_FILE_CONFLICT=70), and UI
indicators in ProjectHeader + StatusBar. 170/170 tests pass.
Health tick now self-stops when no tracked project has a running/starting
agent session. Auto-restarts on next recordActivity() call. Eliminates
5-second polling overhead when all agents are idle/done.