feat: config loader with validation and tilde expansion

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

bin/config.py

@@ -0,0 +1,20 @@
+import os
+import yaml
+
+CONFIG_PATH = os.path.expanduser('~/.claude/autoresearch.yaml')
+DEFAULTS = {'time_limit_minutes': 10, 'benchmarks': []}
+
+class ConfigError(Exception):
+    pass
+
+def load_config(path=CONFIG_PATH):
+    with open(path) as f:
+        cfg = yaml.safe_load(f)
+    if not cfg or 'projects' not in cfg or not cfg['projects']:
+        raise ConfigError(f"'projects' list is required in {path}")
+    for p in cfg['projects']:
+        p.setdefault('benchmarks', DEFAULTS['benchmarks'])
+        p.setdefault('time_limit_minutes', DEFAULTS['time_limit_minutes'])
+        p['path'] = os.path.expanduser(p['path'])
+    cfg.setdefault('token_threshold', {'context_remaining_pct': 60, 'api_budget_usd': 5.0})
+    return cfg