Adds Coverage (harmonic reach) + Redundancy (Tarjan articulation) axes +
composite & grade. Closes#672.
**TDD note (BLOCKER-1):** Community PR delivered as a single squashed
commit, so there is no separate pre-fix failing-test commit — please
accept as a community-PR exemption. The tests are *gating*, not just
thorough: each axis test pins a specific topology outcome (coverage on
line/star/disconnected/weight-sensitive; redundancy
online/triangle/star/bridged-cliques), and an end-to-end `/api/nodes`
surface test drives the whole pipeline and asserts the composite
diverges from the Traffic axis. Inverting the `1/weight` distance,
dropping the NaN/Inf reject, removing the `redundancyMinWeight` floor,
or aliasing `usefulness_score` back onto `traffic_share_score` each
break a specific assertion. The axis functions are pure (no hidden
state), so the suite fully characterises the behavior without the red
anchor.
Co-authored-by: Waydroid Builder <build@waydroid.local>
