chore: scaffold Cargo workspace for the Ghostty rewrite

Start of the full Rust rewrite of Ghostty 1.3.1 (reference source in
../ghostty). Sets up a workspace whose crates mirror Ghostty's Zig modules
(vt, unicode, datastruct, os, input, config, terminal, font, renderer,
termio, core, apprt-gtk) so porting work can proceed in parallel per crate.

Also adds:
- docs/rewrite/{ARCHITECTURE,PLAN,STATUS,AGENT_GUIDE}.md: crate map, core
  design decisions (safe Rust, slab-based PageList, logical capacity
  accounting), phased plan, progress tracker, and porting rules.
- Workspace clippy config relaxing pedantic lints that are pure noise for
  low-level terminal code (casts, long functions).
- Shared vt types needed by several work packages up front: kitty
  keyboard flags (kitty/key.rs) and the CSI separator bitset (SepList).

Test Plan:
- cargo test -p ghostty-vt (3 tests pass)
- cargo clippy -p ghostty-vt --all-targets -- -D warnings

crates/ghostty-renderer/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "ghostty-renderer"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[dependencies]
+ghostty-config.workspace = true
+ghostty-font.workspace = true
+ghostty-terminal.workspace = true
+
+[lints]
+workspace = true