Release 0.18.1: native text selection in chat

[mostlydev]

Restores native text selection in tt chat.

Summary

• Mouse capture is off by default, so drag-select, double-click and copy work natively again, including in herdr.
• tt chat --mouse opts back into wheel scrolling, trading away native selection. --no-mouse still takes precedence.
• Keyboard scrolling (PgUp/PgDn, Shift+↑/↓, Ctrl+End) is unchanged. Help, usage and README are updated.

Verification

• npm run typecheck, npm test (572 passed, 1 skipped), npm run build, git diff --check, npm pack --dry-run