feat: implement Trello authentication & connection plugin

Add TrelloClient for Trello REST API interaction with env-var-based
credential management (TRELLO_API_KEY, TRELLO_TOKEN).

Implements:
- trello_verify_credentials — verify API key/token against Trello API
- trello_list_boards — list accessible Trello boards
- trello_disconnect — clear in-memory credentials

Includes full test suite (18 tests), spec document, and plugin metadata.

Issue: #1

README.md

@@ -1,3 +1,95 @@
 # trello-plugin
 
-Hermes Agent plugin for Trello board integration
+Hermes Agent plugin for Trello board integration.
+
+## Setup
+
+### 1. Get Trello Credentials
+
+1. Get your **API Key** from: https://trello.com/app-key
+2. Generate a **Token** from the same page (click "Token" under API Key)
+3. Set these as environment variables in your Hermes profile config (`.env` or `config.yaml`):
+
+```bash
+export TRELLO_API_KEY="your-trello-api-key"
+export TRELLO_TOKEN="your-trello-token"
+```
+
+### 2. Install
+
+```bash
+cd trello-plugin
+pip install .
+```
+
+For development:
+
+```bash
+pip install -e ".[dev]"
+```
+
+### 3. Register with Hermes Agent
+
+Add the plugin to your Hermes config (`~/.hermes/config.yaml` or profile):
+
+```yaml
+plugins:
+  - trello-plugin
+```
+
+## Available Tools
+
+Once configured, the agent has access to these tools:
+
+### `trello_verify_credentials`
+Verifies your Trello API key and token are valid by calling the Trello API.
+
+```
+✓ Trello credentials verified successfully (authenticated as your-username)
+```
+
+### `trello_list_boards`
+Lists all Trello boards accessible with your credentials.
+
+| Field | Description |
+|-------|-------------|
+| `id` | Trello board ID |
+| `name` | Board name |
+| `url` | Direct Trello URL |
+| `closed` | Whether the board is archived |
+| `starred` | Whether the board is starred |
+
+### `trello_disconnect`
+Clears Trello credentials from the in-memory client. Since credentials are stored in environment variables, the agent can reconnect automatically on the next tool call.
+
+## Development
+
+```bash
+# Install dev dependencies
+pip install -e ".[dev]"
+
+# Run tests
+PYTHONPATH=src python3 -m pytest tests/ -v
+
+# Lint
+pip install ruff
+ruff check src/
+```
+
+## Architecture
+
+```
+trello-plugin/
+├── src/
+│   └── trello_plugin/
+│       ├── __init__.py    # Package exports
+│       ├── client.py      # TrelloClient — REST API wrapper
+│       └── tools.py       # Hermes tool definitions
+├── tests/
+│   └── test_auth.py       # Test suite (18 tests)
+├── docs/
+│   └── backend/
+│       └── trello-auth-spec.md
+├── pyproject.toml
+└── README.md
+```