refactor: merge CLI requirements to central requirements

- Remove duplicate /opt/aitbc/cli/requirements.txt file
- All CLI dependencies already covered in central requirements.txt
- Central requirements has newer versions of all CLI dependencies
- Update workflow documentation to reflect central venv usage
- Update environment configuration to use /etc/aitbc/.env
- Remove duplicate dependency management

This consolidates all Python dependencies in the central requirements.txt
and eliminates the need for separate CLI requirements management.

apps/blockchain-node/src/aitbc_chain/config.py

@@ -16,7 +16,7 @@ class ProposerConfig(BaseModel):
     max_txs_per_block: int
 
 class ChainSettings(BaseSettings):
-    model_config = SettingsConfigDict(env_file="/opt/aitbc/.env", env_file_encoding="utf-8", case_sensitive=False, extra="ignore")
+    model_config = SettingsConfigDict(env_file="/etc/aitbc/.env", env_file_encoding="utf-8", case_sensitive=False, extra="ignore")
 
     chain_id: str = ""
     supported_chains: str = "ait-devnet" # Comma-separated list of supported chain IDs