archive: Move JIT/Cranelift to archive during Phase 15 focus

Phase 15 requires concentrated development on PyVM and LLVM backends only.
JIT/Cranelift was causing build confusion and distracting AI developers.

## Archived Components
- src/jit/ → archive/jit-cranelift/src/jit/
- src/backend/cranelift/ → archive/jit-cranelift/src/backend/cranelift/
- JIT Box modules → archive/jit-cranelift/src/boxes/
- JIT scripts → archive/jit-cranelift/scripts/, tools/
- clif_adapter.rs → archive/jit-cranelift/src/semantics/

## Build Changes
- Cargo.toml: Comment out cranelift-jit feature and dependencies
- src/lib.rs: Disable JIT module declaration
- src/boxes/mod.rs: Disable JIT Box module declarations
- src/semantics/mod.rs: Disable clif_adapter module
- debug_box.rs: Replace JIT calls with archive stubs

## Documentation
- archive/jit-cranelift/ARCHIVE_NOTES.md: Complete restoration guide
- Reason: Phase 15 selfhosting focus (80k→20k line reduction)
- Restoration: Full procedure documented for future revival

This eliminates build errors and AI developer confusion, enabling
focused Phase 15 development on PyVM/LLVM backends only.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

archive/jit-cranelift/src/jit/mod.rs

@@ -0,0 +1,16 @@
+//! JIT subsystem: Cranelift-based JIT manager and lowering stubs
+
+pub mod abi;
+pub mod boundary;
+pub mod config;
+pub mod engine;
+pub mod events;
+pub mod r#extern;
+pub mod hostcall_registry;
+pub mod lower;
+pub mod manager;
+pub mod observe;
+pub mod policy;
+pub mod rt;
+pub mod semantics;
+pub mod shim_trace;