feat(tui): add width_method config option for ZWJ emoji handling

[Flare576]

Problem

ZWJ emoji sequences (family emoji, profession emoji, pride flag, etc.) cause layout corruption in terminals that don't render them as joined glyphs — most notably tmux, but also many older terminals. Text after a ZWJ sequence shifts across the screen, wraps incorrectly, and input box spacing breaks.

This affects anyone running OpenCode inside tmux with a pane split, and is a long-standing source of reports (see #6210).

Solution

OpenTUI's Zig layer already has a fully implemented and tested no_zwj width calculation mode that handles this correctly. This PR exposes it as a user-configurable option via opencode.json.

Depends on: anomalyco/opentui#751 — which wires no_zwj through the TypeScript→FFI chain. No default is changed in OpenTUI; this PR just passes the user's preference through.

Changes

• packages/opencode/src/config/tui-schema.ts: Add width_method to TuiOptions schema ("unicode" | "wcwidth" | "no_zwj", optional)
• packages/opencode/src/cli/cmd/tui/app.tsx: Pass input.config.width_method to the render() call as widthMethod

Usage

Users experiencing layout corruption add one line to their opencode.json:

{
  "tui": {
    "width_method": "no_zwj"
  }
}

Behavior

no_zwj breaks ZWJ-joined emoji into their component glyphs (👩‍🚀 renders as 👩 + 🚀), which is visually imperfect but correctly laid out. Skin tone modifiers, regional indicator flags, combining accents, and CJK characters are completely unaffected.

Mode	Effect
unicode (default)	ZWJ sequences as single glyph — correct on modern terminals, corrupts tmux
no_zwj (opt-in)	ZWJ sequences split — safe everywhere, slightly less pretty
wcwidth	Existing option, unchanged

No Breaking Changes

Default is still "unicode". Users who don't set width_method see identical behavior to today.

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