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/ansi.rs

@@ -0,0 +1,156 @@
+//! ANSI types (ZIG/src/terminal/ansi.zig).
+
+/// C0 (7-bit) control characters from ANSI.
+///
+/// This is not complete, control characters are only added to this
+/// as the terminal emulator handles them.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(u8)]
+pub enum C0 {
+    /// Null
+    Nul = 0x00,
+    /// Start of heading
+    Soh = 0x01,
+    /// Start of text
+    Stx = 0x02,
+    /// Enquiry
+    Enq = 0x05,
+    /// Bell
+    Bel = 0x07,
+    /// Backspace
+    Bs = 0x08,
+    /// Horizontal tab
+    Ht = 0x09,
+    /// Line feed
+    Lf = 0x0A,
+    /// Vertical Tab
+    Vt = 0x0B,
+    /// Form feed
+    Ff = 0x0C,
+    /// Carriage return
+    Cr = 0x0D,
+    /// Shift out
+    So = 0x0E,
+    /// Shift in
+    Si = 0x0F,
+}
+
+impl C0 {
+    /// Convert from a raw byte; unknown values return `None` (the Zig enum
+    /// is non-exhaustive).
+    pub fn from_int(v: u8) -> Option<Self> {
+        Some(match v {
+            0x00 => Self::Nul,
+            0x01 => Self::Soh,
+            0x02 => Self::Stx,
+            0x05 => Self::Enq,
+            0x07 => Self::Bel,
+            0x08 => Self::Bs,
+            0x09 => Self::Ht,
+            0x0A => Self::Lf,
+            0x0B => Self::Vt,
+            0x0C => Self::Ff,
+            0x0D => Self::Cr,
+            0x0E => Self::So,
+            0x0F => Self::Si,
+            _ => return None,
+        })
+    }
+}
+
+/// The SGR rendition aspects that can be set, sometimes known as attributes.
+/// The value corresponds to the parameter value for the SGR command (ESC [ m).
+/// Non-exhaustive in Zig; `Other` carries unknown values.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum RenditionAspect {
+    Default,
+    Bold,
+    DefaultFg,
+    DefaultBg,
+    Other(u16),
+}
+
+impl RenditionAspect {
+    pub fn from_int(v: u16) -> Self {
+        match v {
+            0 => Self::Default,
+            1 => Self::Bold,
+            39 => Self::DefaultFg,
+            49 => Self::DefaultBg,
+            v => Self::Other(v),
+        }
+    }
+}
+
+/// The device attribute request type (ESC [ c).
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum DeviceAttributeReq {
+    /// Blank
+    Primary,
+    /// >
+    Secondary,
+    /// =
+    Tertiary,
+}
+
+/// Possible cursor styles (ESC [ q)
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CursorStyle {
+    Default,
+    BlinkingBlock,
+    SteadyBlock,
+    BlinkingUnderline,
+    SteadyUnderline,
+    BlinkingBar,
+    SteadyBar,
+}
+
+/// The status line type for DECSSDT. Non-exhaustive in Zig.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum StatusLineType {
+    None,
+    Indicator,
+    HostWritable,
+    Other(u16),
+}
+
+impl StatusLineType {
+    pub fn from_int(v: u16) -> Self {
+        match v {
+            0 => Self::None,
+            1 => Self::Indicator,
+            2 => Self::HostWritable,
+            v => Self::Other(v),
+        }
+    }
+}
+
+/// The display to target for status updates (DECSASD).
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum StatusDisplay {
+    Main,
+    StatusLine,
+}
+
+/// The possible modify key formats to ESC[>{a};{b}m
+/// Note: this is not complete, we should add more as we support more
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ModifyKeyFormat {
+    Legacy,
+    CursorKeys,
+    FunctionKeys,
+    OtherKeysNone,
+    OtherKeysNumericExcept,
+    OtherKeysNumeric,
+}
+
+/// The protection modes that can be set for the terminal. See DECSCA and
+/// ESC V, W.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ProtectedMode {
+    Off,
+    /// ESC V, W
+    Iso,
+    /// CSI Ps " q
+    Dec,
+}