aletheia: clippy -D warnings has 25 findings — add as blocking gate once clean

[hyperpolymath]

Split out of #123. Root rust-ci.yml gates build, unit tests, formatting and the
zero-dependency constraint, but not clippy, because clippy is currently red and a
non-blocking lint job is a fake gate.

Measured

cargo clippy --all-targets -- -D warnings -> 25 errors

By class:

count	class
6	function is never used
4	field is never read
2	unnecessary .iter() variant use
2	can be simplified
1	variants Gold/Platinum never constructed
1	unwrap_or_else to construct default
1	unused variable
1	unnecessary closure

Note on sequencing

The majority are dead-code findings with the same root cause as the integration-test
failures — modules that main.rs never wires up. Fix that first; most of these
disappear on their own. What remains is a handful of genuine simplifications.

Do not silence these with a crate-level #![allow(dead_code)] — that would hide the
fact that a third of the crate is unreachable, which is the actual signal here.

Once clean, add clippy to root rust-ci.yml as a blocking job.