refactor: remove AIEOS identity support

- Remove src/identity/ directory (aieos.rs, mod.rs)
- Remove IdentityConfig struct and identity field from Config
- Remove build_system_prompt_with_identity and load_aieos_from_config functions
- Remove AIEOS-related imports from channels/mod.rs
- Remove identity module declarations from main.rs and lib.rs
- Remove AIEOS tests from config/schema.rs
- Keep OpenClaw markdown-based identity as the only supported format

This simplifies the codebase by removing unused AIEOS complexity.
All 832 tests pass.

src/main.rs

@@ -22,7 +22,6 @@ mod doctor;
 mod gateway;
 mod health;
 mod heartbeat;
-mod identity;
 mod integrations;
 mod memory;
 mod migration;