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

pyproject.toml

@@ -0,0 +1,35 @@
+[build-system]
+requires = ["setuptools>=64"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "trello-plugin"
+version = "0.1.0"
+description = "Hermes Agent plugin for Trello board integration"
+requires-python = ">=3.12"
+license = {text = "MIT"}
+dependencies = [
+    "requests>=2.31",
+]
+
+[project.optional-dependencies]
+dev = [
+    "pytest>=8",
+    "pytest-cov>=5",
+    "requests-mock>=1.12",
+    "ruff>=0.4",
+]
+
+[tool.setuptools.packages.find]
+where = ["src"]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+python_files = ["test_*.py"]
+
+[tool.ruff]
+line-length = 100
+target-version = "py312"
+
+[tool.ruff.lint]
+select = ["E", "F", "I", "N", "W", "UP", "PL"]