refactor(terminal): wire kitty graphics and drop PageList workarounds

Integration pass over the terminal core (Codex/gpt-6-astra, reviewed):
- Screen now owns the real kitty ImageStorage; new/reset/teardown,
  erase-display deletes and alternate-screen limit inheritance hook in
  where Zig does, and Terminal implements ExecTerminal so kitty APC
  commands execute against it. Exec tests use a real Terminal.
- The PageList gains the APIs Screen/Terminal needed (pin iterators,
  cross-page row/partial-row clone, string allocator probing, dedup
  before allocating hyperlinks, Top viewport fixup after erase, append_
  grapheme no longer marking rows dirty), and the Screen/Terminal
  workarounds for their absence are removed so the code mirrors Zig.

Public signatures are unchanged; downstream crates build as before.

Test Plan:
- cargo test -p ghostty-terminal (1252 passed, 0 ignored)
- cargo clippy -p ghostty-terminal --all-targets -- -D warnings

crates/ghostty-terminal/src/render.rs

@@ -20,9 +20,12 @@
 //! To use this, initialize the render state to empty, then call `update`
 //! on each frame to update the state to the latest terminal state.
 //!
-//! ```ignore
+//! ```
+//! # use ghostty_terminal::{render::RenderState, terminal::{Terminal, Options}};
+//! # let mut terminal = Terminal::new(Options::new(80, 24))?;
 //! let mut state = RenderState::new();
 //! state.update(&mut terminal)?;
+//! # Ok::<(), ghostty_terminal::page::Error>(())
 //! ```
 //!
 //! Note: the render state retains as much memory as possible between updates