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-unicode/build.rs

@@ -18,6 +18,7 @@ mod props;
 mod ucd;
 
 use std::env;
+use std::fmt::Write as _;
 use std::fs;
 use std::path::PathBuf;
 
@@ -31,6 +32,7 @@ fn main() {
     println!("cargo:rerun-if-changed=src/lut.rs");
     println!("cargo:rerun-if-changed=src/props.rs");
     println!("cargo:rerun-if-changed=ucd");
+    println!("cargo:rerun-if-changed=ucd/CaseFolding.txt");
 
     let ucd = ucd::Ucd::load(&ucd_dir);
 
@@ -54,4 +56,52 @@ fn main() {
         emoji.write_rust("bool", ToString::to_string),
     )
     .unwrap();
+
+    generate_case_folding(&ucd_dir, &out);
+}
+
+/// Generates `case_folding_full.rs` from `CaseFolding.txt`: the `C` (common)
+/// and `F` (full) statuses, which is uucode's `case_folding_full`.
+fn generate_case_folding(ucd_dir: &std::path::Path, out: &std::path::Path) {
+    let text = fs::read_to_string(ucd_dir.join("CaseFolding.txt")).unwrap();
+    let mut entries: Vec<(u32, Vec<u32>)> = Vec::new();
+    for line in text.lines() {
+        let line = line.split('#').next().unwrap().trim();
+        if line.is_empty() {
+            continue;
+        }
+        let fields: Vec<&str> = line.split(';').map(str::trim).collect();
+        if fields.len() < 3 || (fields[1] != "C" && fields[1] != "F") {
+            continue;
+        }
+        let cp = u32::from_str_radix(fields[0], 16).unwrap();
+        let mapping: Vec<u32> = fields[2]
+            .split_whitespace()
+            .map(|v| u32::from_str_radix(v, 16).unwrap())
+            .collect();
+        assert!(!mapping.is_empty() && mapping.len() <= 3);
+        entries.push((cp, mapping));
+    }
+    entries.sort_by_key(|e| e.0);
+    entries.dedup_by_key(|e| e.0);
+
+    let mut src = String::new();
+    writeln!(
+        src,
+        "static CASE_FOLDING_FULL: [(u32, [u32; 3]); {}] = [",
+        entries.len()
+    )
+    .unwrap();
+    for (cp, m) in &entries {
+        let mut a = [0u32; 3];
+        a[..m.len()].copy_from_slice(m);
+        writeln!(
+            src,
+            "    ({cp:#x}, [{:#x}, {:#x}, {:#x}]),",
+            a[0], a[1], a[2]
+        )
+        .unwrap();
+    }
+    src.push_str("];\n");
+    fs::write(out.join("case_folding_full.rs"), src).unwrap();
 }