fix: systematic byte fidelity for config strings and RV7 gaps

Resolves the 9 gap groups in docs/rewrite/notes/review-rv7-codex.md and
audits every string-typed config field against its consumers
(field -> consumers -> decode status table in final-Z9.md):
- Windows EnvMap keys use a port of Zig's nls.zig uppercase table
  (upcaseW); Windows locale init follows Zig's chain (setlocale +
  _putenv_s); malformed WTF-8 now fails process launch conversions like
  Zig instead of substituting U+FFFD; kitty file paths convert WTF-8.
- bash --rcfile/--init-file, configured TERM and inherited GTK LANG
  keep their original bytes.
- C API clipboard completion and ghostty_surface_binding_action take
  bytes; complete_clipboard_request is byte-typed through the core.
- text:/csi:/esc: bindings, enquiry-response, input = path:, embedded
  initial_input, search needles, titles, link regexes, clipboard
  codepoint map, command palette text and GTK font/namespace values
  decode the escape encoding before use.

Remaining by design: D-Bus a{ss} values and +new-window arguments are
UTF-8 by D-Bus type. C API key/preedit text follows separately.

Test Plan:
- cargo test --workspace
- just check-macos (both), just check-windows, just check-wasm

crates/ghostty-termio/src/command_windows.rs

@@ -50,6 +50,8 @@ use crate::windows_args::{self, create_windows_env_block, windows_create_command
 /// Errors from [`Command::start`].
 #[derive(Debug, thiserror::Error)]
 pub enum StartError {
+    #[error("malformed wtf-8 in a path, argument or environment value")]
+    InvalidWtf8(#[from] ghostty_os::osbytes::InvalidWtf8),
     #[error("string or environment is not valid unicode")]
     Encode(#[from] windows_args::EncodeError),
     #[error("windows error: {0}")]
@@ -131,16 +133,22 @@ impl Command {
     pub fn start(&mut self) -> Result<(), StartError> {
         // `path` and `args` are the config command's argv strings (encoded
         // OS strings); decode them to WTF-16 for the Windows API.
-        let application_w = EncodedOs::from_encoded(&self.path).to_wide_nul();
-        let cwd_w = self.cwd.as_ref().map(EncodedOs::to_wide_nul);
+        // Like Zig's fallible `utf8ToUtf16Le*`, malformed input fails the
+        // launch instead of selecting a U+FFFD-substituted path or argument.
+        let application_w = EncodedOs::from_encoded(&self.path).try_to_wide_nul()?;
+        let cwd_w = self
+            .cwd
+            .as_ref()
+            .map(EncodedOs::try_to_wide_nul)
+            .transpose()?;
         let mut command_line_w = if self.args.is_empty() {
             None
         } else {
             let wide: Vec<Vec<u16>> = self
                 .args
                 .iter()
-                .map(|a| EncodedOs::from_encoded(a).to_wide())
-                .collect();
+                .map(|a| EncodedOs::from_encoded(a).try_to_wide())
+                .collect::<Result<_, _>>()?;
             let mut line = windows_create_command_line_wide(&wide);
             line.push(0);
             Some(line)