refactor(config): parse config values from raw bytes like Zig

Zig parses config values (cli/args.zig, Config.zig field parsers,
config/string.zig) from raw byte slices, and each field type decides
whether it requires UTF-8 (InvalidValue otherwise) or stores bytes. The
port escape-encoded raw bytes into Strings at the line reader and let
fields parse the escaped text, so fields could observe encoding
artifacts; successive audits kept finding such leaks (RV5-RV8).

Field parsers now receive the original bytes: text fields validate UTF-8
where Zig does, byte/path fields store bytes (EncodedOs/OsString). This
resolves all 9 RV8 findings (docs/rewrite/notes/review-rv8-codex.md),
each with a regression test: Windows path conversion fails with
BadPathName instead of substituting U+FFFD; Windows process launch uses
strict UTF-8 like Zig's Command; the WTF-8 decoder accepts paired-
surrogate encodings like Zig; literal U+FDD0 Unicode key triggers;
selection-word-chars and clipboard-codepoint-map reject invalid UTF-8;
font style / codepoint-map family names use original bytes; C title
actions forward bytes; D-Bus new-window/Flatpak conversions match Zig.
Design, sweep and validation: docs/rewrite/notes/final-bytes-refactor.md.

Also moves the bundled iTerm2-Color-Schemes license out of
resources/themes/ so +list-themes no longer lists it as a theme
(output is now byte-identical to Ghostty 1.3.1).

Done by Codex (gpt-6-astra), reviewed and verified by the orchestrator.

Test Plan:
- cargo test --workspace --no-fail-fast (3428 passed, exit 0)
- just check-macos (both), just check-windows, just check-wasm
- +show-config --default --docs, +list-keybinds, +list-actions --docs,
  +list-themes --plain compared with /usr/bin/ghostty

docs/rewrite/notes/cleanup-V2.md

@@ -3,7 +3,7 @@
 ## Resources (self-contained)
 - `resources/` mirrors Ghostty's `share/ghostty` plus its sibling `share/terminfo`:
   `shell-integration/`, `themes/` (463 files copied from the installed Ghostty 1.3.1,
-  `themes/LICENSE-iTerm2-Color-Schemes` = MIT attribution, written from the upstream license;
+  `LICENSE-iTerm2-Color-Schemes` = MIT attribution, written from the upstream license;
   no upstream copy existed on this machine, check the copyright line if it matters) and
   `terminfo/` (compiled `xterm-ghostty`, `g/ghostty`).
 - `scripts/gen-terminfo.sh` (`just terminfo`): `cargo run -p ghostty-termio --example terminfo`