Smooth move-repeat pointer movement

[enaboapps]

Summary

• replace interval-sized move-repeat jumps with an 8 ms continuous motion scheduler
• accumulate time-scaled fractional displacement into physical pixel deltas
• provide an immediate directional pixel for short presses and debit it from later movement
• preserve existing pointer-speed, acceleration, movement-interval, scroll-repeat, overlay, and cleanup behavior on Windows and macOS

Root cause

Move repeat injected the entire scaled command delta immediately and again after every configured movement interval. Smoothstep changed the size of each jump, but did not make the movement continuous.

Compatibility

• no protocol changes
• no persisted settings changes
• one-off pointer movement is unchanged
• scrolling and scroll repeat are unchanged

Validation

• npm run lint
• npm test (57 Vitest tests and 5 update-feed tests)
• npm run build
• cargo fmt --manifest-path src-tauri/Cargo.toml --check
• cargo clippy --manifest-path src-tauri/Cargo.toml --all-targets -- -D warnings
• cargo test --manifest-path src-tauri/Cargo.toml (145 unit tests and 2 integration tests)

Closes #583