fix(terminal): refit grid after enabling WebGL

[Yt4aZaveta]

Problem

When a terminal card switched from the DOM renderer to WebGL, xterm kept the grid fitted for the DOM cell width. WebGL snaps cells to device pixels, so the existing PTY dimensions could leave a visible empty strip on the right and make the terminal appear narrowed.

Change

Refit the terminal immediately after WebGL is attached, using the existing fit and PTY resize path. DOM and WebGL renderer transitions now both fit with the active renderer.

Validation

• npm test — 1282 passed, 0 failed, 2 skipped.
• npm run typecheck — passed.
• npm run build — passed.
• Manual Electron/xterm/node-pty A/B check: DOM 116 columns; fixed WebGL 123 columns, real PTY stty size reported 29 123; repeated renderer cycles, scrollback, alternate screen, focus, context loss, and teardown passed with no console or renderer errors.
• Checked open PRs: feat(agents): delegation rules, an OS isolation layer and per-CLI modes #109 and perf: smaller app, cheaper canvas and terminals, faster startup, hidden surfaces paused #112; the patch applies cleanly and neither includes this WebGL refit.