Windows popup suppression, Night Shift improvements

[AlanKharebov]

Summary

Suppress console popup windows on Windows and improve Night Shift reliability and progress reporting.

Changes

• Suppress subprocess console windows on Windows (CREATE_NO_WINDOW across all subprocess calls)
• Suppress Claude SDK subprocess popups (anyio.open_process patch)
• Align default model fallback to claude-sonnet-4-6
• Require active head before triggering Night Shift
• Emit per-project progress events during harvest
• Emit per-file and per-chunk progress events during extraction
• Increase progress event buffer from 100 to 5000

Branch

cortex/suppress-popups-hardcoded-heads