fix(forkchoice-viz): always render finalized block as fully filled (lambdaclass#339)

## 🗒️ Description / Motivation

The fork choice visualization currently renders the finalized block as
empty. This happens because each node is filled proportionally to its
`weight` value. This value is computed by the
[compute_block_weights()](https://github.com/lambdaclass/ethlambda/blob/main/crates/blockchain/fork_choice/src/lib.rs#L5-L27)
method, which returns 0 for the `start_slot` (which is always the
finalized block's slot).

The reported `0` is technically accurate but misleading: a finalized
block has full validator support by definition (2/3 supermajority and
unbroken justified chain). However, this is only misleading for the
visualisation, since `compute_block_weights()` correctly skips the
finalized block because LMD GHOST treats it as the root of the
fork-choice tree, not a candidate, so weighing it adds no information to
head selection.

Proposed solution: render finalized blocks as fully filled green discs
and show `status: finalized` in the tooltip instead of `weight: 0`.

<img width="311" height="154" alt="Screenshot 2026-05-01 at 14 31 15"
src="https://github.com/user-attachments/assets/13dfcae7-0178-49ca-9308-4dd3a82019a4"
/>


## What Changed
 - `crates/net/rpc/static/fork_choice.html`:
- `nodeRatio`: returns `1` for blocks at or below `finalized.slot`, so
they render as solid green discs.
- Tooltip shows `status: finalized` for finalized blocks instead of
`weight: 0`.

## Correctness / Behavior Guarantees
- Only the forkchoice visualization changes; consensus and weight
computation are unchanged.
- Non-finalized blocks still fill proportionally to `weight /
validator_count`.
- Finalized blocks show up as fully filled. When hovering on a finalized
block, there's a status field associated showing: `status: finalized`.


## Tests Run
- Manual: ran a single-node devnet and confirmed finalized blocks render
as solid green discs with `status: finalized` in the tooltip.

## Related Issues / PRs
- Closes lambdaclass#333

---------

Co-authored-by: Pablo Deymonnaz <pdeymon@fi.uba.ar>

Author: conache

crates/net/rpc/static/fork_choice.html

@@ -391,12 +391,14 @@
 
       const flatNodes = allDescendants.map(d => {
         const roles = nodeRoles(d.data, data);
+        // Finalized blocks are filled by default, otherwise scale by fork-choice weight.
+        const isFinalized = roles.includes("finalized");
         return {
           ...d.data,
           x: d.x,
           y: d.y,
           _color: roles.length > 0 ? COLORS[roles[0]] : COLORS.default,
-          _ratio: weightRatio(d.data, data.validator_count),
+          _ratio: isFinalized ? 1 : weightRatio(d.data, data.validator_count),
           // Colors of secondary roles, in priority order (after the primary).
           _haloColors: roles.slice(1).map(r => COLORS[r])
         };