feat(vt): port Ghostty's VT parsing layer

Ports the parsing half of ZIG/src/terminal into the ghostty-vt crate:
- Parser state machine with a compile-time generated parse table and
  the UTF-8 decoder
- OSC parser incl. all sub-parsers (titles, colors, clipboard, hyperlinks,
  semantic prompts/OSC 133, OSC 9 / ConEmu, iTerm2, kitty clipboard,
  color and text-sizing protocols, context signals)
- CSI, SGR, modes table with save/restore, charsets, ansi, device status,
  mouse shapes, APC, DCS (incl. XTGETTCAP), tmux control-mode parser
- color palette / X11 color names, kitty color and graphics command parser

Deviations from Zig (documented in docs/rewrite/notes/ghostty-vt-W*.md):
parser actions own their payloads instead of borrowing parser buffers;
OSC strings are Vec<u8>; non-exhaustive Zig enums gain an Other(raw)
variant; tmux regexes replaced by equivalent hand-written matchers.

Known follow-up: semantic_prompt.rs carries local copies of the printf-q
and percent decoders that belong in ghostty-os.

Test Plan:
- cargo test -p ghostty-vt: 395 passed, 1 ignored (skipped in Zig too)
- cargo clippy -p ghostty-vt --all-targets -- -D warnings: clean

docs/rewrite/notes/ghostty-vt-W1.md

@@ -0,0 +1,21 @@
+# ghostty-vt W1 notes
+
+## Ported (Zig -> Rust, under crates/ghostty-vt/src)
+- Parser.zig -> parser.rs (`Parser`, `State`, `TransitionAction`, `Action`, `Csi`/`Esc`/`Dcs`, `MAX_PARAMS`, `SepList`)
+- parse_table.zig -> parse_table.rs (`TABLE`, built by `const fn`; identical rule order)
+- UTF8Decoder.zig -> utf8_decoder.rs (`Utf8Decoder::next -> (Option<u32>, bool)`)
+- osc.zig -> osc/mod.rs; osc/encoding.zig -> osc/encoding.rs; osc/parsers/*.zig -> osc/parsers/*.rs (all 15)
+- color.zig -> color.rs; x11_color.zig -> x11_color.rs (res/rgb.txt copied, `include_str!`, lazy map); kitty/color.zig -> kitty/color.rs
+
+## Deviations / API notes
+- `Action` owns its data (fixed inline arrays) rather than borrowing from the parser: use `csi.params()`, `csi.intermediates()`, `csi.final_`, `csi.params_sep`. `Print(u32)`. `Parser::next` returns `[Option<Action>; 3]`.
+- `Parser::new()`; `parser.osc_parser.alloc` is a `bool` ("allocator available", Zig `?Allocator`). Stream must set `osc_parser.alloc = true` as stream.zig does, otherwise OSC 4/5/10-19/104/110-119/133/21 are rejected like in Zig.
+- OSC `Command` is a Rust enum (`osc::Command`, `osc::Key` via `Command::key()`); `[:0]const u8` fields are `Vec<u8>` (no NUL, not necessarily UTF-8). `Parser::end` returns an owned `Option<Command>`.
+- Fixed buffer (MAX_BUF=2048, one byte reserved for NUL where Zig writes one) vs allocating writer = one `Vec<u8>` with an optional cap. `Parser::data()` (reserves NUL) / `buffered()` (does not) replace `writer.buffered()`. Remaining edge: osc9/iterm2/text_sizing use `data()` even where Zig writes no NUL for some sub-commands (only differs at exactly 2048 payload bytes).
+- semantic_prompt: `Option` enum is `OptionKey`; `printf_q_decode`/`url_percent_decode` local copies (TODO(integration): move to/consume from ghostty-os string_encoding). `color::Rgb` (alias `RGB`); `DynamicRgb.override` is `override_`.
+- Clippy: test modules `#![allow(clippy::unwrap_used)]`.
+
+## Skipped tests
+- `ghostty.h Command.ProgressReport.State` (C ABI), `refAllDecls`/`test { _ = ... }` comptime-reference tests, comptime `@sizeOf(Command)` assert.
+- One iterm2 test is `SkipZigTest` in Zig; kept as `#[ignore]`.
+- Extra tests added: osc_112 in color parser, printf-q decode in semantic_prompt.