Restore rustfmt and clippy cleanliness

[willwashburn]

Problem

The workspace tests pass, but the repository is not currently clean under standard Rust hygiene checks:

• cargo fmt --all -- --check reports formatting diffs across CLI and SDK files.
• cargo clippy --workspace --all-targets -- -D warnings fails with mechanical style issues and some cleanup signals: module_inception, large enum variants, derivable defaults, unnecessary clones/casts/unwraps, overindented docs, and stale helper shapes.

This makes routine review harder and lets non-idiomatic code accumulate.

Relevant files

Examples from the current run include:

• crates/relayburn-sdk/src/analyze/context_delta.rs
• crates/relayburn-sdk/src/analyze/span_tree.rs
• crates/relayburn-sdk/src/ingest.rs
• crates/relayburn-sdk/src/reader/claude/span_tree.rs
• crates/relayburn-sdk/src/query_verbs.rs
• crates/relayburn-cli/src/commands/flow.rs

Suggested scope

Keep this mechanical and removal-oriented:

• Run rustfmt and commit only formatting changes plus minimal fixes needed for clippy.
• Prefer deleting stale comments and deriving defaults over adding allows.
• Where a clippy warning points to a real design smell, simplify locally rather than broad refactoring.
• Add CI steps for cargo fmt --all -- --check and cargo clippy --workspace --all-targets -- -D warnings only if the team wants those enforced going forward.

Definition of done

• cargo fmt --all -- --check passes.
• cargo clippy --workspace --all-targets -- -D warnings passes, or intentional exceptions are narrowly allowed with comments.
• cargo test --workspace still passes.