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/version.rs

@@ -92,7 +92,13 @@ mod tests {
     #[test]
     fn version_output_layout() {
         let mut buf = Vec::new();
-        write_version(&mut buf, &BuildInfo::default(), false).unwrap();
+        let info = BuildInfo {
+            version_string: "1.3.1".into(),
+            commit: None,
+            release_channel: "stable".into(),
+            ..BuildInfo::default()
+        };
+        write_version(&mut buf, &info, false).unwrap();
         let s = String::from_utf8(buf).unwrap();
         assert!(s.starts_with(
             "Ghostty 1.3.1\n\nVersion\n  - version: 1.3.1\n  - channel: stable\nBuild Config\n"