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-core/src/lib.rs

@@ -1 +1,33 @@
-//! ghostty-core: see docs/rewrite/ARCHITECTURE.md for the module map.
+//! ghostty-core: the terminal application core (`App.zig`, `Surface.zig`,
+//! `surface_mouse.zig`, `global.zig`). See `docs/rewrite/notes/ghostty-core.md`.
+//!
+//! The core is runtime-agnostic: it talks to the app runtime (GTK) through
+//! the traits in `ghostty_apprt::runtime_api` and implements
+//! [`CoreApp`](ghostty_apprt::runtime_api::CoreApp) /
+//! [`CoreSurface`](ghostty_apprt::runtime_api::CoreSurface).
+
+#![cfg_attr(test, allow(clippy::unwrap_used, clippy::assert_is_empty))]
+// Faithful port of long Zig functions with many Result-returning callbacks.
+#![allow(
+    clippy::nonminimal_bool,
+    clippy::question_mark,
+    clippy::unnecessary_wraps,
+    clippy::struct_field_names,
+    clippy::needless_pass_by_value,
+    clippy::needless_pass_by_ref_mut,
+    clippy::collapsible_if,
+    clippy::assigning_clones,
+    clippy::items_after_statements,
+    clippy::type_complexity,
+    clippy::too_many_arguments,
+    clippy::wildcard_imports,
+    clippy::manual_let_else
+)]
+
+pub mod app;
+pub mod global;
+pub mod surface;
+pub mod surface_mouse;
+
+pub use app::App;
+pub use surface::Surface;