fix: restore CJK wide character support in ZerolagInput overlay

[TeigenZhang]

Summary

• Add charCellWidth / stringCellWidth helpers to overlay-renderer.ts — prefers xterm Unicode11 addon's getStringCellWidth, falls back to Unicode range detection for CJK/fullwidth characters
• Fix makeLine — use for...of iterator (proper Unicode code point iteration) with visual column offset positioning; wide characters get 2 * cellW span width
• Fix renderOverlay cursor — use stringCellWidth instead of string.length for cursor column calculation
• Fix _render line splitting — replace String.slice with visual-column-width-aware splitting to prevent CJK characters overflowing line boundaries
• Extend XtermTerminal type with unicode property; add terminal to RenderParams for width detection passthrough
• Bump asset version query strings (?v=0.3.0 → ?v=0.3.1a) for cache invalidation

Context

The xterm-zerolag-input package refactor (extracting LocalEchoOverlay into ZerolagInputAddon) lost the CJK wide character handling from PR #13. All characters were assumed to be 1 cell wide, causing Chinese/Japanese/Korean text to overlap during input.

Files Changed

File	Change
packages/xterm-zerolag-input/src/types.ts	Add unicode to XtermTerminal, terminal to RenderParams
packages/xterm-zerolag-input/src/overlay-renderer.ts	Add width helpers; fix makeLine and renderOverlay for CJK
packages/xterm-zerolag-input/src/zerolag-input-addon.ts	Fix _render line splitting; pass terminal to renderer
src/web/public/index.html	Bump ?v= for cache invalidation

Test plan

• Type Chinese text (e.g., via pinyin IME) — characters should not overlap during input
• Verify CJK text renders with correct double-width spacing in the overlay
• Test Japanese (こんにちは) and Korean (안녕하세요) input
• Verify cursor positions correctly after CJK characters
• Verify long CJK input wraps to next line at correct column boundary
• Verify existing ASCII input is unaffected
• Test teammate terminal panels also render CJK correctly

[Ark0N]

Sorry about this — the CJK wide character support was lost during the refactor. I'll implement a clean fix directly on master that preserves the existing 4-space indentation style and only touches the lines that need to change.

[Ark0N]

Merged via direct commit to master. All 124 tests pass, typecheck clean, lint/format clean.

[Ark0N]

Test plan executed ✅

Added comprehensive CJK test suite in d79e25d covering all 7 test plan items (51 tests, all passing):

#	Item	Tests
1	Chinese text — no character overlap	4
2	CJK double-width spacing	8
3	Japanese (こんにちは) + Korean (안녕하세요) input	14
4	Cursor positioning after CJK characters	6
5	Line wrapping at correct column boundary	6
6	ASCII input unaffected (regression)	7
7	Teammate terminal panels render CJK correctly	6

File: packages/xterm-zerolag-input/test/cjk-testplan.test.ts

Note on Test 7: Teammate panels share the same global xterm-zerolag-input.js vendor bundle — no separate copy. Tests verify the addon works identically across separate terminal instances.