fix(tests): pass base_url explicitly in AIAgent constructor calls

Tests that construct AIAgent(api_key=..., ...) without base_url were
relying on provider-resolver fallback state from other tests in the
same xdist worker. When matrix-split distributed them to different
shards, the resolver found no env vars and no config and raised
'No LLM provider configured'.

Fix: add base_url='https://openrouter.ai/api/v1' to every AIAgent
construction that passes api_key. AIAgent.__init__ with both args set
takes the direct-construction path (line 960 in run_agent.py) and
skips resolver fallback entirely, making these tests self-contained.

7 files, 16 call sites updated via AST-based fixup. One call site
(test_none_base_url_passed_as_none) left alone — that test's
intent is to verify base_url=None behavior, so adding base_url
defeats the test.

Validation:
- tests/run_agent/ full run: 760 passed, 0 failed (was 1 failure
  under the AST script's over-application, now clean)
- Matrix shard 3 local run: 3083 passed, 0 failed, 1m44s

tests/run_agent/test_plugin_context_engine_init.py

@@ -45,6 +45,7 @@ def test_plugin_engine_gets_context_length_on_init():
 
         agent = AIAgent(
             api_key="test-key-1234567890",
+            base_url="https://openrouter.ai/api/v1",
             quiet_mode=True,
             skip_context_files=True,
             skip_memory=True,
@@ -75,6 +76,7 @@ def test_plugin_engine_update_model_args():
         agent = AIAgent(
             model="openrouter/auto",
             api_key="test-key-1234567890",
+            base_url="https://openrouter.ai/api/v1",
             quiet_mode=True,
             skip_context_files=True,
             skip_memory=True,