feat: replace CRDT pre blocks with purpose-built convergence visualizations

Each of the four CRDTs in the Domain Registry now renders as a compact HTML diagram showing its specific convergence story rather than raw text output (which was overflowing its container):

- ORSet: side-by-side concurrent add/remove replicas → join result with "add-wins" annotation - LWWRegister: stacked write timeline with winner badge → commutative join result - GCounter: proportional bar chart per agent slot → component-wise max total - VectorClock: grid of clock cells (self/zero/max) with ⊕ symbol → concurrent_with badge and merged clock

All values remain live-computed from _compute_crdt_demos(); the HTML visualization is generated alongside the existing text output field and selected via html_output key in _render_capability_card.