Fix terminal URL activation gesture

[FloSch62]

Summary

• apply the configured terminal link activation gesture to web URLs as well as file paths
• keep non-matching clicks available for terminal text selection
• clear incidental selections after a URL is deliberately opened
• rename the setting label to Open terminal links and document that it covers both link types

Why

Terminal web URLs were handled directly by the xterm web-links callback, bypassing the modifier checks used by terminal file links. As a result, an ordinary click could open a URL while the default file-link behavior required Alt + left click.

This makes URL and file-link interactions consistent and preserves normal click and double-click text selection.

Closes #134.

Validation

• pnpm exec vitest run unit/client/terminal-file-links.test.ts — 28 tests passed
• full unit suite — 931 tests passed, 3 skipped
• pnpm typecheck
• pnpm lint