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

docs/rewrite/STATUS.md

@@ -0,0 +1,17 @@
+# Status
+
+Legend: ⬜ todo · 🟨 in progress · ✅ done (gate passed, committed) · ⚠️ done with gaps
+
+| WP | Scope | Owner | State | Notes |
+|---|---|---|---|---|
+| P0 | scaffolding | opus | ✅ | |
+| W1 | vt: parser/osc/color | sonnet | ⬜ | |
+| W2 | vt: csi/sgr/modes/kitty/apc/dcs | sonnet | ⬜ | |
+| W3 | unicode + datastruct | sonnet | ⬜ | |
+| W4 | os | sonnet | ⬜ | |
+| W5 | input | sonnet | ⬜ | |
+| W6 | config | sonnet | ⬜ | |
+| W7 | font: metrics + sprite | sonnet | ⬜ | |
+
+## Log
+- 2026-10-11: Phase 0 complete; Phase 1 launched.