fix: close remaining gaps found by the completeness audit

Addresses the partial ports listed in
docs/rewrite/notes/review-completeness-codex.md (details in
docs/rewrite/notes/gaps-X2.md):
- Flatpak: the exit watcher no longer consumes the host command; a
  shared FlatpakSignalHandle lets closing a surface still SIGHUP the
  host process group.
- Child environment is byte-preserving end to end (ghostty_os::EnvMap
  of OsStrings) and Snap paths are filtered like filterSnapPaths.
- argv handling no longer panics on non-UTF-8 arguments.
- URI percent-decoding keeps raw bytes; OSC 7 pwd is passed through
  without lossy conversion.
- Keybinding comparison/hashing uses full Unicode case folding from a
  table generated from CaseFolding.txt (Unicode 17.0.0).
- Link regexes set Oniguruma's whole-search retry limit through the new
  minimal ghostty-onig crate (one SAFETY-commented FFI call).
- OSC 9 NUL-capacity check ordering matches Zig.
- Wayland registry binds/clears globals advertised after startup.
- Custom shaders may pass sampler2D to helper functions (naga adapter).
- +list-themes preview renders OSC 8 links, styled underlines and
  follows color-scheme reports.

Also includes the inspector's integration edits in shared files
(renderer state hook, termio VT recording, core/apprt-gtk wiring), X1's
config/input/cli additions for completion generation, and a fix for a
race in the termio backpressure test (it wrote before `stty raw`
applied, so the cooked line discipline dropped bytes past MAX_CANON).

Test Plan:
- cargo test --workspace
- cargo clippy --workspace --all-targets -- -D warnings

crates/ghostty-cli/src/build_info.rs

@@ -49,15 +49,11 @@ pub struct BuildInfo {
 impl Default for BuildInfo {
     fn default() -> Self {
         BuildInfo {
-            version_string: "1.3.1".to_string(),
-            commit: None,
-            release_channel: "stable".to_string(),
-            build_mode: if cfg!(debug_assertions) {
-                ".Debug"
-            } else {
-                ".ReleaseFast"
-            }
-            .to_string(),
+            // Derived by `build.rs` (git describe / workspace app-version).
+            version_string: env!("GHOSTTY_VERSION_STRING").to_string(),
+            commit: Some(env!("GHOSTTY_COMMIT").to_string()).filter(|c| !c.is_empty()),
+            release_channel: env!("GHOSTTY_RELEASE_CHANNEL").to_string(),
+            build_mode: env!("GHOSTTY_BUILD_MODE").to_string(),
             app_runtime: ".gtk".to_string(),
             font_backend: ".fontconfig_freetype".to_string(),
             renderer: "renderer.generic.Renderer(renderer.OpenGL)".to_string(),