fix(tui): enable copy on select by default

[hdosys]

Issue for this PR

Closes #44392

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Restores copy-on-select as the default on Windows, matching the existing behavior on other platforms. Mouse-up now reaches the existing Selection.copy and clipboard path. Setting OPENCODE_EXPERIMENTAL_DISABLE_COPY_ON_SELECT=true still preserves manual Ctrl+C and right-click copy.

How did you verify your code works?

• Checked unset, true, 1, and false flag behavior directly.
• Ran bun typecheck in packages/core and packages/tui.
• Built the Windows x64 standalone executable and passed its version smoke test.
• Sent an SGR mouse selection through Herdr; OpenCode showed the copy toast and the selected text reached the native Windows clipboard.
• Passed the repository pre-push typecheck across all 30 runnable tasks.

Screenshots / recordings

N/A. No visual change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, here are related PRs that might be relevant to this PR (excluding the current PR #44393):

Related PRs:

1. fix(tui): clipboard copy on Linux without external binaries #44394 - fix(tui): clipboard copy on Linux without external binaries

   • Closely related to clipboard functionality, likely part of the same effort to improve copy-on-select behavior across platforms

2. fix(tui): sanitize clipboard text #44197 - fix(tui): sanitize clipboard text

   • Related to clipboard operations and text handling

3. feat(tui): add linux_clipboard_selection config for primary buffer support #32370 - feat(tui): add linux_clipboard_selection config for primary buffer support

   • Related to clipboard selection configuration on Linux

4. fix(tui): surface clipboard write failures instead of false success #41924 - fix(tui): surface clipboard write failures instead of false success

   • Related to clipboard write operations

5. fix(tui): prevent sidebar selection copy bleed #41713 - fix(tui): prevent sidebar selection copy bleed

   • Related to selection and copy behavior in the TUI

These are clipboard and selection-related PRs in the TUI package, though none appear to be exact duplicates of PR #44393. The most closely related appears to be #44394, which addresses clipboard copy on Linux as part of what seems to be a broader effort to improve clipboard handling across platforms.