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-os/src/args.rs

@@ -9,6 +9,17 @@ pub fn iterator() -> std::env::ArgsOs {
     std::env::args_os()
 }
 
+/// Collect the process arguments as `String`s without ever panicking on
+/// non-UTF-8 bytes (invalid sequences become U+FFFD). The CLI/config layers
+/// are string based; `+action` dispatch only depends on the ASCII prefix.
+pub fn collect_lossy() -> Vec<String> {
+    lossy(iterator())
+}
+
+fn lossy(it: impl Iterator<Item = std::ffi::OsString>) -> Vec<String> {
+    it.map(|a| a.to_string_lossy().into_owned()).collect()
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -18,4 +29,15 @@ mod tests {
         let mut iter = iterator();
         assert!(!iter.next().unwrap().is_empty());
     }
+
+    #[test]
+    fn lossy_does_not_panic_on_non_utf8() {
+        use std::os::unix::ffi::OsStringExt;
+        let args = vec![
+            std::ffi::OsString::from("ghostty"),
+            std::ffi::OsString::from_vec(vec![b'+', b'x', 0xff]),
+        ];
+        let out = lossy(args.into_iter());
+        assert_eq!(out, vec!["ghostty".to_owned(), "+x\u{fffd}".to_owned()]);
+    }
 }