feat(core): port App/Surface and wire up the runnable ghostty binary

This is the integration step that turns the ported crates into a working
terminal: `cargo run` now opens a GTK window running the user's shell.

ghostty-core ports App.zig, Surface.zig (split into keyboard, mouse,
binding, clipboard and config submodules), surface_mouse.zig and
global.zig, and implements the runtime traits. perform_binding_action
handles every binding action.

Cross-crate integration:
- The core<->runtime traits (CoreApp, CoreSurface, RtApp, RtSurface,
  Waker) move from apprt-gtk into ghostty_apprt::runtime_api so the core
  stays runtime-agnostic; Scrollbar/RendererHealth stand-ins are replaced
  by the real terminal/renderer types.
- termio now uses ghostty_renderer::state::{State, SharedState}; the
  renderer calls kitty_update; image-storage-limit is applied at init
  and on config change.
- The search thread locks the terminal through a TerminalLock trait so
  it can share the render state mutex; termio's Wakeup gained a hook to
  wake the renderer thread.
- apprt-gtk: GL proc addresses are resolved through libepoxy's
  epoxy_glFoo pointer variables (plain glFoo symbols resolved to null),
  default DPI fixed to 96, libadwaita version read without GTK init so
  --version works headless.

The root binary dispatches +actions to ghostty-cli (list-fonts,
show-face and new-window are now wired) and otherwise runs the GTK app
with the real core.

Verified at runtime on Wayland and X11: shell prompt and colored output
render, child exit closes the window cleanly. Not yet verified: keyboard
and mouse input, clipboard, IME, tabs and splits (no key injection was
possible in this environment). GHOSTTY_DEBUG_SCREENSHOT=<png> dumps the
renderer's last frame for headless checks.

Test Plan:
- cargo test --workspace (2890 passed)
- cargo clippy --workspace --all-targets -- -D warnings
- GSETTINGS_BACKEND=memory GHOSTTY_RESOURCES_DIR=/usr/share/ghostty \
  cargo run

crates/ghostty-apprt/src/surface.rs

@@ -21,28 +21,10 @@ pub const NOTIFICATION_TITLE_LEN: usize = 64;
 /// `[255:0]u8` => 256 bytes including the sentinel.
 pub const NOTIFICATION_BODY_LEN: usize = 256;
 
-// TODO(integration): `terminal.Scrollbar` lives in ghostty-terminal
-// (page_list::Scrollbar); apprt doesn't depend on it. Local stand-in with
-// identical fields.
-/// Scrollbar geometry in rows.
-#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
-pub struct Scrollbar {
-    /// Total scrollable rows.
-    pub total: usize,
-    /// Viewport's offset from the oldest row.
-    pub offset: usize,
-    /// Visible row count.
-    pub len: usize,
-}
-
-// TODO(integration): `renderer.Health` lives in ghostty-renderer
-// (backend::Health); apprt doesn't depend on it.
-/// The health status of a renderer.
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum RendererHealth {
-    Healthy,
-    Unhealthy,
-}
+/// The health status of a renderer (`renderer.Health`).
+pub use ghostty_renderer::backend::Health as RendererHealth;
+/// Scrollbar geometry in rows (`terminal.Scrollbar`).
+pub use ghostty_terminal::page_list::Scrollbar;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum ReportTitleStyle {