Fix test layout parity: orphan flat tests + missing mirrored modules + duplicate suite

[tschm]

Subcategory: Test layout parity (rhiza check_test_layout.py)
Current score: 3/10 → Target: 10/10

Problem

check_test_layout.py fails — the suite is a half-finished migration to the mirrored tests/<pkg>/** layout, leaving orphans, gaps, and a duplicated test module.

Missing mirrored test files:

• tests/pycharting/api/test_interface.py (for src/pycharting/api/interface.py)
• tests/pycharting/api/test_routes.py (for src/pycharting/api/routes.py)
• tests/pycharting/core/test_lifecycle.py (for src/pycharting/core/lifecycle.py)
• tests/pycharting/core/test_server.py (for src/pycharting/core/server.py)

Orphan flat test files (no matching src/* module):

• tests/test_api_routes.py, tests/test_data_ingestion.py, tests/test_data_slicing.py, tests/test_import.py, tests/test_interface.py, tests/test_lifecycle.py, tests/test_server.py

Duplicate execution: tests/test_data_ingestion.py (513 lines) and tests/pycharting/data/test_ingestion.py (781 lines) both cover data/ingestion.py and both run — wasteful and confusing.

Fix

Consolidate every flat test into the mirrored layout under tests/pycharting/** (merging the richer mirrored ingestion file, dropping the stale flat duplicate), so each src/pycharting/<mod>.py has exactly one tests/pycharting/<mod>/test_*.py (or matching name).

Done when

• python3 <rhiza>/scripts/check_test_layout.py exits 0 ("tests mirror sources 1:1") and no module is tested by two files.