Remove legacy loader pipeline alias shim

[Teagan42]

What

• remove the LegacyLoaderPipeline shim from mcp_plex.loader so the legacy class is no longer exposed via an alias
• update loader unit and logging tests to construct the staged orchestrator helpers directly and validate the new log output
• refresh the loader alias regression test to assert the alias is gone

Why

• the legacy alias is being retired in favour of the staged orchestrator helpers, so tests must target the new integration points

Affects

• loader initialisation helpers and their associated unit/logging alias regression tests

Testing

• uv run pytest

Documentation

• not needed

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https://chatgpt.com/codex/tasks/task_e_68e3394e63548328ad75d64b82893b68

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
mcp_plex/loader
__init__.py	783	228	71%	183–190, 239, 325–330, 932–933, 955–999, 1017, 1023, 1028–1068, 1073–1075, 1084–1094, 1097–1103, 1111–1143, 1151–1164, 1167–1181, 1184–1198, 1201–1214, 1219–1250, 1255–1288, 1291–1295, 1300–1308, 1317–1324, 1329, 1339–1342, 1378, 1391, 1510–1512, 1576–1593, 1935
mcp_plex/loader/pipeline
__init__.py	15	7	53%	57–62, 68
channels.py	73	2	97%	19–20
enrichment.py	337	43	87%	78, 80, 87, 91, 170, 191, 211, 219–221, 228–231, 234–236, 244, 301, 357, 380, 384, 386, 412, 430, 442, 471, 477, 480–488, 514, 538, 609, 612–614
ingestion.py	81	8	90%	67, 98–108, 129, 157, 179
orchestrator.py	85	5	94%	48, 112, 141, 164–165
persistence.py	124	9	93%	112, 154–155, 165, 170, 174–176, 214
mcp_plex/server
__init__.py	614	29	95%	43–44, 119–120, 148, 252, 256, 277–280, 297, 362, 365, 402, 420–421, 458, 1109, 1131–1137, 1173, 1191, 1196, 1214, 1338, 1375
__main__.py	4	4	0%	3–8
config.py	48	7	85%	50, 52–55, 65, 76
TOTAL	2366	342	86%

Tests	Skipped	Failures	Errors	Time
128	0 💤	0 ❌	0 🔥	59.914s ⏱️