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-termio/tests/exec_integration.rs

@@ -287,9 +287,13 @@ fn large_write_with_backpressure_is_delivered_in_order() {
     // queue (the pty buffer is far smaller) and the output reader at the
     // same time (cat would otherwise block on a full pty).
     let mut f = start(
-        sh("stty raw -echo; head -c 262144 | wc -c; echo done"),
+        sh("stty raw -echo; echo ready; head -c 262144 | wc -c; echo done"),
         |_| {},
     );
+    // Writing before `stty raw` applies would go through the cooked-mode
+    // line discipline, which silently drops bytes past MAX_CANON (4095)
+    // on a line without a newline.
+    f.wait_text("ready");
     let chunk = vec![b'x'; 4096];
     for _ in 0..64 {
         f.write(&chunk);
@@ -555,7 +559,7 @@ fn change_config_message_updates_palette_and_colors() {
 fn process_output_manual_api() {
     // Termio can also be fed manually (no child involved).
     let config = base_config();
-    let mut ecfg = exec::Config::new(std::collections::HashMap::new(), "xterm-256color");
+    let mut ecfg = exec::Config::new(ghostty_os::EnvMap::new(), "xterm-256color");
     ecfg.command = Some(sh("true"));
     let (tx, _rx) = unbounded();
     let termio = Termio::init(Options {