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

crates/ghostty-vt/src/csi.rs

@@ -0,0 +1,91 @@
+//! CSI command enums (ZIG/src/terminal/csi.zig).
+
+/// Modes for the ED CSI command.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(u8)]
+pub enum EraseDisplay {
+    Below = 0,
+    Above = 1,
+    Complete = 2,
+    Scrollback = 3,
+    /// This is an extension added by Kitty to move the viewport into the
+    /// scrollback and then erase the display.
+    ScrollComplete = 22,
+}
+
+impl EraseDisplay {
+    /// Non-exhaustive in spirit: unknown values yield `None`.
+    pub fn from_int(v: u16) -> Option<Self> {
+        Some(match v {
+            0 => Self::Below,
+            1 => Self::Above,
+            2 => Self::Complete,
+            3 => Self::Scrollback,
+            22 => Self::ScrollComplete,
+            _ => return None,
+        })
+    }
+}
+
+/// Modes for the EL CSI command. Non-exhaustive in Zig so that conversion
+/// never fails since the inputs are user-generated; `Other` carries the raw value.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum EraseLine {
+    Right,
+    Left,
+    Complete,
+    RightUnlessPendingWrap,
+    Other(u8),
+}
+
+impl EraseLine {
+    pub fn from_int(v: u8) -> Self {
+        match v {
+            0 => Self::Right,
+            1 => Self::Left,
+            2 => Self::Complete,
+            4 => Self::RightUnlessPendingWrap,
+            v => Self::Other(v),
+        }
+    }
+}
+
+/// Modes for the TBC (tab clear) command. Non-exhaustive like [`EraseLine`].
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum TabClear {
+    Current,
+    All,
+    Other(u8),
+}
+
+impl TabClear {
+    pub fn from_int(v: u8) -> Self {
+        match v {
+            0 => Self::Current,
+            3 => Self::All,
+            v => Self::Other(v),
+        }
+    }
+}
+
+/// Style formats for terminal size reports (XTWINOPS).
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum SizeReportStyle {
+    Csi14T,
+    Csi16T,
+    Csi18T,
+    Csi21T,
+}
+
+/// XTWINOPS CSI 22/23
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct TitlePushPop {
+    pub op: TitlePushPopOp,
+    pub index: u16,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum TitlePushPopOp {
+    Push,
+    Pop,
+}