docs: label test file and add TEST_EXPENSES_AGENT.md

Adds module-level label and cross-reference to the new doc.
TEST_EXPENSES_AGENT.md documents every test group, case, and the
real-world bug each test guards against (e.g. In-N-Out OCR mismatch).

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

tests/test_expenses_agent.py

@@ -1,12 +1,31 @@
 """
-Unit tests for ExpensesAgent logic.
+ActiveBlue AI — Expenses Agent Unit Tests
+==========================================
+Suite:   test_expenses_agent.py
+Module:  agent_service/agents/expenses_agent.py
+         agent_service/tools/receipt_parser.py
+         addons/activeblue_ai/models/ab_ai_mail.py
 
-Covers:
-  - _find_semantic_duplicate  (two-pass dedup algorithm)
-  - _plan()                   (keyword detection → user_confirmed, user_dup_decision)
-  - _act() confirmation gate  (enters awaiting_confirmation before writing records)
-  - parse_upload              (ZIP extraction, filename date parsing)
-  - _text_to_html             (HTML escaping and newline conversion)
+Purpose
+-------
+Verify the core business logic of the expenses agent without requiring
+a live Odoo instance, database, or LLM.  All external dependencies
+(ORM, HTTP, Ollama) are mocked.  Tests run in < 1 second.
+
+Run
+---
+    source .venv-test/bin/activate
+    python -m pytest tests/test_expenses_agent.py -v
+
+Test groups
+-----------
+  TestFindSemanticDuplicate  — two-pass duplicate-detection algorithm
+  test_plan_*                — intent keyword → user_confirmed / user_dup_decision
+  test_act_*                 — _act() confirmation gate and expense creation
+  TestParseUpload            — receipt_parser ZIP handling and metadata
+  TestTextToHtml             — HTML escaping (skipped without Odoo env)
+
+See tests/TEST_EXPENSES_AGENT.md for full documentation.
 """
 from __future__ import annotations