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-apprt-gtk/Cargo.toml

@@ -10,6 +10,7 @@ ghostty-apprt.workspace = true
 ghostty-config.workspace = true
 ghostty-input.workspace = true
 ghostty-datastruct.workspace = true
+ghostty-inspector.workspace = true
 ghostty-os.workspace = true
 ghostty-vt.workspace = true
 log = "0.4"
@@ -28,13 +29,14 @@ half = "2"
 libc = "0.2.190"
 signal-hook = "0.4.5"
 libloading = "0.9.0"
+dear-imgui-glow = "0.19"
+glow = "0.18"
 
 [build-dependencies]
 glib-build-tools = "0.22"
 
 [dev-dependencies]
 env_logger = "0.11"
-glow = "0.18"
 
 [lints.rust]
 unsafe_code = "deny"