Use idiomatic casing per context across all wire protocols

Background

Different layers of the ecosystem have different idiomatic conventions:

• Swift (Stori) — camelCase, as per Swift/JSON convention
• JSON wire protocol — camelCase (Swift clients expect it)
• Python backend (Maestro, MuseHub) — snake_case per PEP 8

Currently there is inconsistency. For example, MuseHub hub API returns snake_case JSON keys (repo_id, default_branch) while some callers (agent scripts, CLI one-liners) accidentally use camelCase (repoId, defaultBranch) from GitHub/gh muscle memory.

Task

Sweep all wire protocol boundaries and enforce idiomatic casing per context:

1. MuseHub JSON API responses — audit all response shapes; confirm snake_case throughout
2. Swift/Stori client — confirm camelCase on the wire; add CodingKeys or convertFromSnakeCase decoder strategy if bridging to a snake_case backend
3. Maestro — confirm internal Python structures are snake_case; confirm any JSON serialized for Swift clients is camelCase
4. Agent scripts / CLI tooling — update any hardcoded camelCase key lookups against MuseHub API to snake_case

Acceptance criteria

• No camelCase keys in MuseHub Python response models
• No snake_case keys sent over the wire to Swift clients
• A note in the relevant agent-guide.md or API docs clarifying the casing contract at each boundary