feat: carry role-child fields in the protocol crate (lockstep)

[saucam]

Lockstep half of highflame-ai/codeoid#256 (collaboration role-children, P1b). CONTRIBUTING requires this crate to move in the same change set as the daemon's packages/protocol/.

What changed

• write: Option<bool> on CollaborationRole. None/false = read-only. The default is load-bearing: the daemon turns it into a leaf identity carrying no write scope plus a hard tool-deny at its fence, so a reviewer provably cannot write rather than being asked not to. Write authority is opt-in per role.
• New CollaborationRoleRef + collaboration_role on SessionInfo — parent session id, role name, ordinal, write. The mirror of collaboration (set on the orchestrating parent), so the TUI can group a fleet without inferring membership from session names.
• Six SessionInfo fixtures gain collaboration_role: None.

PROTOCOL_VERSION stays at 1

Same reasoning as #35: purely additive optional fields with #[serde(default, skip_serializing_if = "Option::is_none")]. CONTRIBUTING calls the protocol additive-safe and lib.rs scopes the bump to breaking changes; bumping one side alone would manufacture a mismatch warning against a fully compatible daemon.

Verification

• cargo build, cargo clippy --all-targets, cargo test --workspace all green — 354 tests.
• No new clippy warnings: 7 before, 7 after on codeoid-protocol (verified by stashing the change and re-running, not by eyeballing).
• The wire_format SessionInfo fixture now populates collaboration_role. A real session is either a parent or a child, never both — populated anyway so the recursive camelCase walker visits parentSessionId/roleName and would catch a rename_all slip on the new struct.

Follow-up (not here)

Nothing renders these yet. A read-only child and a writing child look identical in the TUI, and a fleet shows as N unrelated sessions. Surfacing the grouping — and especially the write/read-only distinction, since that is a real capability difference — is worth its own PR against the session list and title.

🤖 Generated with Claude Code

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.