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-config/src/macros.rs

@@ -31,6 +31,8 @@ pub struct FieldInfo<T> {
     pub name: &'static str,
     /// Raw doc comment lines.
     pub doc: &'static [&'static str],
+    /// Classification of the field's type (for completion generation).
+    pub kind: crate::cli_args::FieldKind,
     /// Deep equality of this field between two structs.
     pub eq: fn(&T, &T) -> bool,
     /// Format this field as in `+show-config`.
@@ -139,6 +141,7 @@ macro_rules! config_struct {
                     $crate::macros::FieldInfo {
                         name: $key,
                         doc: &[$($doc),*],
+                        kind: <$ty as $crate::cli_args::ConfigField>::KIND,
                         eq: |a: &$name, b: &$name| a.$field == b.$field,
                         format: |a: &$name, name: &str, w: &mut dyn ::core::fmt::Write| {
                             let mut f = $crate::formatter::EntryFormatter::new(name, w);
@@ -268,6 +271,9 @@ macro_rules! config_packed {
         }
 
         impl $crate::cli_args::ConfigField for $name {
+            const KIND: $crate::cli_args::FieldKind =
+                $crate::cli_args::FieldKind::Packed(Self::NAMES);
+
             fn parse_cli(
                 &mut self,
                 value: ::core::option::Option<&str>,