refactor(broker): fold fbuild-broker crate into fbuild-daemon module (#560)

[zackees]

Summary

Resolves#560. fbuild stays as close to a monocrate as possible: the standalone fbuild-broker crate introduced by #559 is removed and its protocol/service/session modules now live under crates/fbuild-daemon/src/broker/. Stacked on feat/v1-broker-adoption so the diff is just the fold, not a re-review of #559.

• No more fbuild-broker crate. The running-process v1 adoption is a module inside fbuild-daemon (the tokio process that actually adopts the broker session), matching how per-platform orchestrators live under fbuild-build.
• register_payload_protocol! pin and RUNNING_PROCESS_DISABLE=1 rollback preserved exactly — the macro pin stays in broker/protocol.rs (the real consumer); the escape-hatch test moved with session.rs.
• CLI diagnostic keeps working without depending on the daemon.fbuild-cli is a thin HTTP client and must not depend on fbuild-daemon, so the dependency-free pieces the daemon running-process diagnostic prints — CacheRoots + the display constants (CI_TRUSTED_INSTANCE, MIN_VERSION, FBUILD_PAYLOAD_PROTOCOL, FBUILD_PROTOCOL_VERSION) — moved into fbuild-paths::running_process. A drift test asserts the daemon's macro pin equals the fbuild-paths display copy.
• New-crate lint guard.crate-gate.yml runs ci/check_workspace_crates.py, which fails CI if [workspace] members gains an entry outside the approved allowlist (a justified new crate must be added to the allowlist in the same PR with rationale).
• Monocrate policy documented in CLAUDE.md and crates/CLAUDE.md.

Test plan

• soldr cargo check --workspace --all-targets — clean; Cargo.lock no longer references fbuild-broker
• soldr cargo clippy -p fbuild-daemon -p fbuild-paths -p fbuild-cli --all-targets -- -D warnings — clean (only the pre-existing MSRV-config notice)
• soldr cargo test -p fbuild-paths -p fbuild-daemon --lib — all 15 broker tests pass in their new home, including payload_protocol_matches_paths_display_copy (drift guard) and disable_env_and_unreachable_broker_contracts (rollback)
• uv run python ci/check_workspace_crates.py — OK: 14 approved members, no new crates; verified it flags an unexpected member
• CI green on crate-gate.yml

🤖 Generated with Claude Code

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