surface: respect semantic prompt boundaries for links (#12435)

Link detection currently expands the clicked location to a full line
before running the configured regexes. When semantic prompt markers are
present, this can cause prompt text and neighboring content to be
matched together even though they are distinct semantic regions.

Use semantic prompt boundaries when selecting the text to inspect for
link matching. This keeps prompt text separate from the content beside
it and avoids folding prompt text into double-click link/path selection.

Add a regression test that models a prompt and command on the same line
and verifies the prompt region and input region remain separate.

----

this is a fix for the issue users reported in
https://github.com/ghostty-org/ghostty/discussions/11415

**disclaimer**: I used codex addon within Cursor to research this
bug/regression and find a proper fix for it.

src/Surface.zig

@@ -4302,7 +4302,9 @@ fn linkAtPin(
     const line = screen.selectLine(.{
         .pin = mouse_pin,
         .whitespace = null,
-        .semantic_prompt_boundary = false,
+        // Respect semantic prompt boundaries so link/path matching doesn't
+        // merge shell prompt content with the text beside it.
+        .semantic_prompt_boundary = true,
     }) orelse return null;
 
     var strmap: terminal.StringMap = undefined;