Add architecture documentation for coglet crates
- crates/README.md: Overall architecture, prediction flow, startup
sequence, bridge protocol, directory structure
- crates/coglet/README.md: Detailed coglet internals, components,
health states, behaviors (shutdown, cancellation, slot poisoning)
- crates/coglet-python/README.md: Python bindings details, active()
flag, single async loop, stdout/stderr routing, audit hook, cancel
