Add configuration for reranker model

[Teagan42]

Summary

• add a reranker_model setting with an environment alias and defaults
• ensure the server and CLI use the configured reranker model when initializing
• document the new reranker override option in the README

Testing

• uv run pytest tests/test_server_config_additional.py::test_settings_defaults_reranker_model
• uv run pytest tests/test_server.py::test_ensure_reranker_uses_thread_executor
• uv run pytest tests/test_server_config_additional.py::test_settings_defaults_reranker_model tests/test_server.py::test_ensure_reranker_uses_thread_executor

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https://chatgpt.com/codex/tasks/task_e_68eae95d405883289337211f5ddb5bec

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
mcp_plex/loader
__init__.py	182	11	94%	139, 209, 323–325, 327, 416–435
qdrant.py	198	2	99%	338–343
samples.py	41	3	93%	55–57
mcp_plex/loader/pipeline
enrichment.py	520	75	86%	234, 255–261, 314, 319, 350, 352, 359, 361, 461, 482, 502, 510–512, 515–519, 522–524, 532–537, 545, 596–597, 621, 679–680, 696, 723, 730, 732, 736, 788, 806, 818, 847, 853, 856–864, 890, 893–895, 912–914, 934–937, 941, 955–959, 981, 983, 986–988
ingestion.py	155	13	92%	82, 133–153, 188, 225, 241, 334, 340, 358
orchestrator.py	95	5	95%	60, 136, 165, 188–189
persistence.py	130	9	93%	123, 165–166, 174, 185, 189–191, 240
mcp_plex/server
__init__.py	395	21	95%	123, 129–132, 151, 157–159, 255, 317, 335–336, 344, 419, 513, 543, 562, 569, 588, 701
cli.py	64	1	98%	78
config.py	83	1	99%	63
media.py	223	21	91%	159–165, 174–177, 215–222, 245, 279, 285, 291, 309–310
mcp_plex/server/tools
media_library.py	337	12	96%	203, 576, 674, 693, 744, 795, 866, 956–960
TOTAL	2954	174	94%

Tests	Skipped	Failures	Errors	Time
201	0 💤	0 ❌	0 🔥	1m 34s ⏱️