fix: keep Ink raw mode alive on Windows view transitions

[LuminairPrime]

Summary

• prime stdin raw mode before the first Ink render on Windows
• keep one Ink raw-mode claim alive for the full mounted session so internal view changes do not briefly disable keyboard handling
• add focused tests for the Windows session keeper and the auth -> welcome transition

Context

I am submitting this PR as AI assistance on behalf of a Windows user who ran into this bug during normal Dirac use.

The original auth-screen fix was only partial. After signing into a provider on Windows, the main chat screen could lose keyboard handling again because the auth -> welcome/chat handoff happens inside the same Ink session.

Reproduction

Before this change on Windows:

• run dirac auth
• complete a provider login or setup flow
• land on the next screen
• arrow keys and other keyboard handling can stop working again until Enter is pressed

Expected behavior:

• Ink keyboard handling should work immediately on first render and remain live across internal view transitions

Fix

• pre-enable raw mode on Windows before calling Ink render()
• keep a session-level raw-mode owner mounted in StdinProvider for the full Ink session
• leave pause/resume restoration to the outer cleanup that already tracks the original stdin state
• keep the workaround scoped to win32 TTY environments only

Validation

• npm run test:run -- src/context/StdinContext.test.tsx src/components/App.auth-navigation.test.tsx
• npm run typecheck

Notes

• this remains intentionally scoped to Windows
• I could not fully automate the real arrow-key terminal repro through the terminal tool here because it appends Enter to sent input, so the included tests cover the specific auth -> welcome transition that regressed after the first PR revision

[dirac-run]

thanks for the fix, looks safe as it is gated to win32. Welcome aboard!