Fix Search schema parity for shows and episodes

[guidefari]

Parent PRD

#9

What to build

Make search() fully support show and episode results end-to-end. The current public types advertise these result kinds, but the runtime schema decoder does not accept them yet, so valid Spotify responses can fail decoding. Keep this focused on parity for existing show and episode search support.

Acceptance criteria

• SearchResponseSchema decodes shows and episodes payloads returned by Spotify
• search() succeeds for show and episode searches without schema mismatches
• Tests cover observable search behavior for show and episode result decoding

Blocked by

None - can start immediately

User stories addressed

• User story 1
• User story 2
• User story 16
• User story 17
• User story 37

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Migrated from guidefari/spotify-effect#55