test(core): add headless end-to-end tests and fix bugs they found

Adds crates/ghostty-core/tests/e2e_*.rs: 81 tests that drive the real
core Surface, termio, pty and child processes through a fake runtime
(recording apprt actions, in-memory clipboard) with a headless renderer
(ghostty-renderer/src/headless.rs). They cover keys (legacy, DECCKM,
kitty, modifyOtherKeys), keybinding actions and sequences, mouse
selection/reporting/scrolling/links, clipboard incl. OSC 52 and paste
safety, resize, focus, titles/pwd/bell/notifications/progress, child
exit, and IME preedit.

Fixes for issues found by the tests and by the Codex audit
(docs/rewrite/notes/review-core-codex.md, all 9 items):
- replacing a selection with copy-on-select panicked (stale tracked
  handles); global new_window no longer inherits a parent; the child
  environment uses the runtime's env wholesale so GTK's removals stick;
  Flatpak host resources path; locale recovery (ensureLocale) in
  apprt-gtk before GTK init and for CLI actions; failed screen-file
  opens propagate errors; OSC 52 base64 rules, CSI/ESC binding length
  limits and GHOSTTY_LOG parsing match Zig.
- Also includes V2's termio cleanups (tmux viewer wiring in the stream
  handler, Pty slave semantics docs, shared cgroup wait loop).

apprt-gtk gains a debug input replay hook (GHOSTTY_DEBUG_INPUT_SCRIPT)
exercising the real GTK key path. With it, the real app was verified on
Wayland: typing and output, new tab, splits, select-all/copy/paste and
font size all work (docs/rewrite/notes/verification-V1.md). Not yet
exercised at GTK level: mouse, real IM-context IME, clipboard dialogs.

Test Plan:
- cargo test --workspace (2983 passed)
- cargo test -p ghostty-core --tests (81 e2e tests)

crates/ghostty-termio/src/exec.rs

@@ -771,10 +771,20 @@ impl Subprocess {
 
             // Assume that the resources directory is adjacent to the terminfo
             // database
-            let parent = std::path::Path::new(base)
-                .parent()
-                .map_or_else(String::new, |p| p.to_string_lossy().into_owned());
-            env.insert("TERMINFO".into(), format!("{parent}/terminfo"));
+            //
+            // Rust-specific: the in-repo dev resources dir (`<ws>/resources`)
+            // carries its compiled terminfo inside itself, so prefer that
+            // when present.
+            let own = format!("{base}/terminfo");
+            let terminfo = if std::path::Path::new(&format!("{own}/x/xterm-ghostty")).exists() {
+                own
+            } else {
+                let parent = std::path::Path::new(base)
+                    .parent()
+                    .map_or_else(String::new, |p| p.to_string_lossy().into_owned());
+                format!("{parent}/terminfo")
+            };
+            env.insert("TERMINFO".into(), terminfo);
         } else {
             env.insert("TERM".into(), "xterm-256color".into());
             env.insert("COLORTERM".into(), "truecolor".into());