fix(windows): use thin LTO to prevent transcription crash

[lemale237]

Summary

• Full LTO (lto = true) causes a STATUS_STACK_BUFFER_OVERRUN (0xc0000409) on Windows when whisper.cpp is invoked during transcription
• The app crashes immediately when the user presses the keyboard shortcut to start recording
• Switching to lto = "thin" eliminates the stack corruption while still providing link-time optimization

Context

This bug was introduced with the Windows build added in #8. The release v0.7.18 Windows installer works fine until the user triggers transcription, at which point the process crashes silently.

The root cause is that full LTO aggressively optimizes across whisper.cpp's C/C++ code and Rust boundaries, causing stack corruption on Windows MSVC builds.

Change

# Before
[profile.release]
lto = true

# After  
[profile.release]
lto = "thin"

Test plan

• Built release binary on Windows 11 x64 with lto = "thin"
• Installed and launched the app successfully
• Pressed keyboard shortcut → transcription works without crash
• Verified transcription output is correct

[lemale237]

The rust-tests CI failure is not related to this change. The errors are pre-existing on main:

• E0428: duplicate mod tests in recorder.rs (lines 359 and 562)
• E0308: type mismatch in run_consumer test call (Vec<f32> vs AudioChunk)

The last CI run on main (#23783797076) also fails with the same errors. This PR only changes lto = true → lto = "thin" in Cargo.toml.