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/mouse_shape.rs

@@ -0,0 +1,125 @@
+//! Mouse cursor shapes (ZIG/src/terminal/mouse_shape.zig).
+
+/// The possible cursor shapes. Not all app runtimes support these shapes.
+/// The shapes are always based on the W3C supported cursor styles so we
+/// can have a cross platform list.
+// Must be kept in sync with ghostty_cursor_shape_e
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default)]
+#[repr(i32)]
+pub enum MouseShape {
+    #[default]
+    Default,
+    ContextMenu,
+    Help,
+    Pointer,
+    Progress,
+    Wait,
+    Cell,
+    Crosshair,
+    Text,
+    VerticalText,
+    Alias,
+    Copy,
+    Move,
+    NoDrop,
+    NotAllowed,
+    Grab,
+    Grabbing,
+    AllScroll,
+    ColResize,
+    RowResize,
+    NResize,
+    EResize,
+    SResize,
+    WResize,
+    NeResize,
+    NwResize,
+    SeResize,
+    SwResize,
+    EwResize,
+    NsResize,
+    NeswResize,
+    NwseResize,
+    ZoomIn,
+    ZoomOut,
+}
+
+impl MouseShape {
+    /// Build cursor shape from string or None if its unknown.
+    pub fn from_string(v: &str) -> Option<MouseShape> {
+        Some(match v {
+            "default" => MouseShape::Default,
+            "context-menu" => MouseShape::ContextMenu,
+            "help" => MouseShape::Help,
+            "pointer" => MouseShape::Pointer,
+            "progress" => MouseShape::Progress,
+            "wait" => MouseShape::Wait,
+            "cell" => MouseShape::Cell,
+            "crosshair" => MouseShape::Crosshair,
+            "text" => MouseShape::Text,
+            "vertical-text" => MouseShape::VerticalText,
+            "alias" => MouseShape::Alias,
+            "copy" => MouseShape::Copy,
+            "move" => MouseShape::Move,
+            "no-drop" => MouseShape::NoDrop,
+            "not-allowed" => MouseShape::NotAllowed,
+            "grab" => MouseShape::Grab,
+            "grabbing" => MouseShape::Grabbing,
+            "all-scroll" => MouseShape::AllScroll,
+            "col-resize" => MouseShape::ColResize,
+            "row-resize" => MouseShape::RowResize,
+            "n-resize" => MouseShape::NResize,
+            "e-resize" => MouseShape::EResize,
+            "s-resize" => MouseShape::SResize,
+            "w-resize" => MouseShape::WResize,
+            "ne-resize" => MouseShape::NeResize,
+            "nw-resize" => MouseShape::NwResize,
+            "se-resize" => MouseShape::SeResize,
+            "sw-resize" => MouseShape::SwResize,
+            "ew-resize" => MouseShape::EwResize,
+            "ns-resize" => MouseShape::NsResize,
+            "nesw-resize" => MouseShape::NeswResize,
+            "nwse-resize" => MouseShape::NwseResize,
+            "zoom-in" => MouseShape::ZoomIn,
+            "zoom-out" => MouseShape::ZoomOut,
+            "left_ptr" => MouseShape::Default,
+            "question_arrow" => MouseShape::Help,
+            "hand" => MouseShape::Pointer,
+            "left_ptr_watch" => MouseShape::Progress,
+            "watch" => MouseShape::Wait,
+            "cross" => MouseShape::Crosshair,
+            "xterm" => MouseShape::Text,
+            "dnd-link" => MouseShape::Alias,
+            "dnd-copy" => MouseShape::Copy,
+            "dnd-move" => MouseShape::Move,
+            "dnd-no-drop" => MouseShape::NoDrop,
+            "crossed_circle" => MouseShape::NotAllowed,
+            "hand1" => MouseShape::Grab,
+            "right_side" => MouseShape::EResize,
+            "top_side" => MouseShape::NResize,
+            "top_right_corner" => MouseShape::NeResize,
+            "top_left_corner" => MouseShape::NwResize,
+            "bottom_side" => MouseShape::SResize,
+            "bottom_right_corner" => MouseShape::SeResize,
+            "bottom_left_corner" => MouseShape::SwResize,
+            "left_side" => MouseShape::WResize,
+            "fleur" => MouseShape::AllScroll,
+            _ => return None,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn cursor_shape_from_string() {
+        assert_eq!(
+            MouseShape::from_string("default"),
+            Some(MouseShape::Default)
+        );
+        assert_eq!(MouseShape::from_string("xterm"), Some(MouseShape::Text));
+        assert_eq!(MouseShape::from_string("nope"), None);
+    }
+}