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/Cargo.toml

@@ -5,14 +5,23 @@ edition.workspace = true
 license.workspace = true
 
 [dependencies]
+base64 = "0.23.1"
+crossbeam-channel = "0.5.17"
+ghostty-apprt.workspace = true
 ghostty-config.workspace = true
-ghostty-terminal.workspace = true
-ghostty-input.workspace = true
-ghostty-font.workspace = true
-ghostty-renderer.workspace = true
-ghostty-termio.workspace = true
-ghostty-os.workspace = true
 ghostty-datastruct.workspace = true
+ghostty-font.workspace = true
+ghostty-input.workspace = true
+ghostty-os.workspace = true
+ghostty-renderer.workspace = true
+ghostty-terminal.workspace = true
+ghostty-termio.workspace = true
+ghostty-unicode.workspace = true
+ghostty-vt.workspace = true
+log = { version = "0.4", features = ["std"] }
+onig = "6.5.3"
+png = "0.18.1"
+thiserror = "2"
 
 [lints]
 workspace = true