feat: map Plex season numbers to TMDb

[Teagan42]

What

• map Plex episodes to TMDb seasons by name or air date when numeric indices differ
• add air_date to TMDBSeason to support year-based mapping
• test season-number resolution using TMDb season air dates

Why

• fixes failed TMDb episode lookups when Plex uses year-indexed seasons like MythBusters

Affects

• loader season resolution
• TMDb season model
• unit tests

Testing

• uv run ruff check .
• uv run pytest

Documentation

• updated AGENTS.md architecture notes

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https://chatgpt.com/codex/tasks/task_e_68c65d89ca6483288426656f49d14b9e

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
mcp_plex
cache.py	36	4	89%	22, 50–52
imdb_cache.py	20	2	90%	17–18
loader.py	290	22	92%	33–35, 86, 99–100, 113, 120, 185, 201, 213, 453–455, 465, 468–472, 597, 852
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	769	50	93%

Tests	Skipped	Failures	Errors	Time
35	0 💤	0 ❌	0 🔥	27.015s ⏱️