test: add tests for setup wizard personalization and system prompt builder

Cover _USE_CASE_PLUGINS mapping, _suggest_plugins side effects, _build_system_base
output for all name/purpose combinations, and GeneralConfig.purpose round-trip.
Also update CLAUDE.md with the testing workflow rule.

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

tests/unit/test_config.py

@@ -55,6 +55,14 @@ def test_general_config_defaults():
     g = GeneralConfig()
     assert g.user_name == "User"
     assert g.assistant_name == "Pyra"
+    assert g.purpose == ""
+
+
+def test_general_config_purpose_roundtrip():
+    from pyra.config.schema import GeneralConfig
+    cfg = GeneralConfig(user_name="Alice", purpose="manage servers")
+    assert cfg.user_name == "Alice"
+    assert cfg.purpose == "manage servers"
 
 
 def test_pyraconfig_has_general_and_plugin_settings():
@@ -70,11 +78,13 @@ def test_config_round_trip_preserves_general(tmp_pyra_home):
     cfg = PyraConfig(ai=ProviderConfig(provider_id="ollama", model="llama3"))
     cfg.general.user_name = "Alice"
     cfg.general.assistant_name = "Aria"
+    cfg.general.purpose = "manage my home server"
     save_config(cfg)
 
     loaded = load_config()
     assert loaded.general.user_name == "Alice"
     assert loaded.general.assistant_name == "Aria"
+    assert loaded.general.purpose == "manage my home server"
 
 
 def test_config_round_trip_preserves_plugin_settings(tmp_pyra_home):