fix(loader): use proper TMDB episode endpoint

[Teagan42]

Summary

• fetch TMDB episode data via tv/{series}/season/{season}/episode/{episode}
• derive season and episode numbers from Plex metadata
• adjust tests for new episode API

Testing

• uv run ruff check .
• uv run pytest

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https://chatgpt.com/codex/tasks/task_e_68c653fcd5808328b48e3a5fb376e003

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
mcp_plex
cache.py	36	4	89%	22, 50–52
loader.py	199	10	95%	32–34, 339, 342–346, 671
server.py	298	22	93%	59–60, 102–103, 226, 454, 458, 480–486, 518, 528, 559–560, 577–578, 601, 604–605, 663
TOTAL	653	36	94%

Tests	Skipped	Failures	Errors	Time
29	0 💤	0 ❌	0 🔥	30.087s ⏱️