fix: render wide characters (CJK/emoji) at double cell width in terminal

[Wirasm]

Summary

• Isolate wide characters (CJK, emoji) into individual text runs so each is positioned at its exact grid column, preventing accumulated width errors in mixed-width lines
• Extend focused cursor to span 2 cell widths when on a wide character
• Fix pre-existing duplicate imports in health.rs and trailing blank line in create.rs

Closes #315

Test plan

• Run echo "Hello 你好世界 World" in embedded terminal — CJK chars render at double width, no gaps/overlaps
• Run echo "Test 🎉🚀 Done" — emoji render at double width, "Done" properly positioned
• Navigate cursor onto a CJK character — cursor spans 2 cell widths
• Pure ASCII content — no visual regression
• cargo test --all passes
• cargo clippy --all -- -D warnings passes

[Wirasm]

PR Review Summary

Critical Issues (0 found)

None.

Important Issues (0 found)

None.

Suggestions (1 found)

Agent	Suggestion	Location
comment-analyzer	Consider expanding the first comment to explain the text shaping vs. grid positioning mismatch (the "why" behind width errors)	terminal_element.rs:388-389

Reviewed & Dismissed

Agent	Finding	Reason Dismissed
code-reviewer	State not reset after wide char continue	False positive — the run_text.is_empty() guard at line 444 already resets all run state for the next character

Strengths

• Clean isolation of wide characters into separate text runs
• Cursor width properly doubled for wide characters
• Existing text run batching sentinel pattern handles state resets correctly
• Minor cleanups (unused imports, trailing blank line) are reasonable housekeeping

Verdict

READY TO MERGE

The wide character rendering fix is correct. Each wide character is isolated into its own BatchedTextRun positioned at its exact grid column, preventing accumulated width errors. The cursor properly spans 2 cells on wide characters. The code integrates cleanly with the existing text run batching state machine.