feat: add cursor blink animation to embedded terminal

[Wirasm]

Summary

• Add 530ms on/off cursor blink to the kild-ui embedded terminal
• Blink resets on every keystroke so the cursor stays solid while typing
• Unfocused cursors remain static (thin bar, no blinking)
• Uses epoch-based timer invalidation to prevent stale timers from toggling state

Implementation

• terminal_view.rs: Added cursor_visible, blink_epoch, _blink_task fields. Spawns blink timer in from_terminal(). reset_blink() called on every keystroke.
• terminal_element.rs: Added cursor_visible parameter. Skips cursor preparation in prepaint when hidden.
• git/health.rs: Fixed pre-existing clippy error (moved test-only imports into #[cfg(test)])

Test plan

• cargo fmt --check && cargo clippy --all -- -D warnings passes
• cargo test --all passes (1676 tests, 0 failures)
• cargo build --all succeeds
• Manual: cursor blinks at ~530ms when terminal is focused
• Manual: cursor stays solid while typing, restarts blink after pause
• Manual: unfocused cursor shows static thin bar (no blinking)

Closes #314

[Wirasm]

PR Review Summary

Critical Issues (1 found)

Agent	Issue	Location
code-reviewer	Initial blink timer can perform one stale toggle after reset_blink() — timer waits 530ms before checking epoch, so if a keystroke fires during the wait, the old timer still executes one toggle	terminal_view.rs:75-92

Important Issues (3 found)

Agent	Issue	Location
code-reviewer	Blink timer loop duplicated verbatim between from_terminal() and reset_blink() — extract to shared method	terminal_view.rs:75-92, 115-131
comment-analyzer	Comment says "always show the thin bar" but cursor_visible only controls whether cursor renders at all, not its style (thin bar is from has_focus in element)	terminal_view.rs:231
silent-failure-hunter	_ => break swallows error details — should match codebase pattern (main_view.rs:187-197) with explicit Ok(false) / Err(e) arms and tracing::debug! logging	terminal_view.rs:79-91, 118-130

Strengths

• Epoch-based timer invalidation is a clean pattern for cancelling stale timers
• Keystroke reset keeps cursor solid while typing (good UX)
• Unfocused cursor logic correctly delegates style to element layer
• health.rs clippy fix properly scopes test-only imports

Verdict

NEEDS FIXES — 1 critical (timer race), 3 important (duplication, misleading comment, silent error swallowing)

Recommended Actions

1. Fix timer race: check epoch before first wait, or accept the one-toggle latency is negligible (530ms max)
2. Extract spawn_blink_timer(cx, epoch) -> Task<()> to deduplicate
3. Fix comment to: // Focused cursors blink; unfocused cursors are always visible (rendered as thin bar in element).
4. Split _ => break into Ok(false) + Err(e) with tracing::debug! for consistency with main_view.rs