feat: openclaw-style secrets (env.vars + \) and per-task model routing

- Replace python-dotenv with config.json env.vars block + \ substitution
- Add models section for per-task model routing (heartbeat, subagent, default)
- Heartbeat/subagent tasks can use different models/providers than main chat
- Remove python-dotenv from dependencies
- Update all docs to reflect new config approach
- Reorganize docs into project/ and research/ subdirectories

pyproject.toml

@@ -26,6 +26,9 @@ test = [
 [project.scripts]
 aetheel = "cli:cli"
 
-[tool.setuptools.packages.find]
+[build-system]
-include = ["agent*", "adapters*", "memory*", "skills*", "scheduler*", "heartbeat*", "hooks*", "webhooks*"]
+requires = ["hatchling"]
-exclude = ["tests*", "archive*", "inspiration*"]
+build-backend = "hatchling.build"
+
+[tool.hatch.build.targets.wheel]
+packages = ["."]