chore(validator): drop .env, keep all config in FastAgent YAMLs

OPENAI_BASE_URL was duplicated between .env and fastagent.config.yaml;
the YAML is authoritative, so .env is dead weight. Removing the .env
template and gitignore entry, updating README to reflect.

The real fastagent.secrets.yaml stays gitignored;
fastagent.secrets.yaml.example remains as the documented schema.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

validator/README.md

@@ -11,26 +11,28 @@ validator/
 ├── pyproject.toml                 # pallas-mcp + fast-agent-mcp deps
 ├── agents.yaml                    # one-agent Pallas topology
 ├── fastagent.config.yaml          # default_model + mnemosyne MCP server
-├── fastagent.secrets.yaml.example # template for the bearer token
-├── .env.example                   # OPENAI_BASE_URL etc.
+├── fastagent.secrets.yaml.example # schema for the (gitignored) secrets file
 └── agents/
     └── mnemosyne_validator.py     # the FastAgent definition
 ```
 
+All configuration lives in the FastAgent YAML files — no `.env` is used. The
+real `fastagent.secrets.yaml` is gitignored; `fastagent.secrets.yaml.example`
+documents its shape and is checked in.
+
 ## Setup
 
 ```bash
 cd validator/
-uv venv .venv
+python3.13 -m venv .venv
 source .venv/bin/activate
-uv pip install -e .
+pip install -e .
 ```
 
-Copy and fill the secrets/env templates:
+Copy the secrets template and fill in the bearer token (see next section):
 
 ```bash
 cp fastagent.secrets.yaml.example fastagent.secrets.yaml
-cp .env.example .env
 ```
 
 ## Provision an MCP bearer token