v1.9.0

What's Changed

• cf4d544 refactor(server): single-source SSE header + JSON response construction
• 0799571 build(deps): Bump github.com/hummingbird-project/hummingbird (#376)
• 9e9b3f3 docs(claude): sync to v1.8.4 and post-release test counts (1041 unit / 477 integration)

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Install: brew install apfel
Upgrade: brew upgrade apfel