Fixes #41

Summary

• Fixes scroll wheel regression in alternate-screen apps (Claude Code, vim, less, htop) introduced in v0.8.4+
• When on the alternate buffer, takes ownership of wheel events and forwards them to the PTY directly instead of relying on xterm's _handleWheel / _handlePassiveWheel which are unreliable after the WebGL context swap
• Sends SGR mouse-wheel sequences (\x1b[<64;col;rowM / \x1b[<65;col;rowM) when the app has enabled mouse tracking, falls back to arrow keys otherwise

Root cause

xterm's built-in wheel forwarding fails in two cases:

1. The wheel listener is only registered when the app has explicitly requested wheel mouse events via DECSET
2. _consumeWheelEvent returns 0 when render-service cell dimensions are temporarily unavailable (can happen after the WebGL renderer swap in v0.8.4+), causing the event to be silently dropped

Test plan

• Scroll in a normal terminal — scrollback works as before
• Scroll inside Claude Code / vim / less — content scrolls correctly
• Scroll in a TUI without mouse tracking enabled — arrow keys sent, content moves

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