fix(react-ui): unify backend-logs entry point for distributed mode

[localai-bot]

Summary

In distributed mode the local `/api/backend-logs` WebSocket has nothing behind it (inference runs on workers), so the "View backend logs" link in Traces dead-ended on `/app/backend-logs/`. Manage worked around it by hiding the action; Traces still rendered the broken link.

This PR makes `/app/backend-logs/:modelId` the single, mode-aware entry point so every view links to the same URL and the destination adapts to the running mode.

• New `BackendLogsRouter` in `BackendLogs.jsx` probes `useDistributedMode` and forks:
  • standalone: existing local WebSocket view (`BackendLogsDetail`), unchanged.
  • distributed: new `DistributedBackendLogsResolver` fans out to each node via `nodesApi.getModels`, filters by `model_name`, then routes:
    • 0 hits - empty state with a link to the Nodes page.
    • 1 hit - `` to `/app/node-backend-logs//`, preserving the `?from=` deep-link timestamp.
    • N hits - picker listing each hosting worker (node id, replica index, load state) so the operator can choose.
• Bare `modelId` in the redirect target intentionally aggregates that node's replicas via the worker's `BackendLogStore`, matching the existing per-node link pattern in `Nodes.jsx`.
• Reverted the per-caller distributed checks now that routing is centralised:
  • `Manage.jsx`: dropped `hidden: distributedMode` on the Backend logs action.
  • `Traces.jsx`: link is unconditional again (no `distributedMode` prop threading).

Any future view that wants to link to backend logs just uses `/app/backend-logs/:modelId` and gets the right behaviour in both modes.

Test plan

• Standalone mode: open Traces, expand a backend trace - "View backend logs" still streams the local model logs as before. Same for Manage > Actions > Backend logs.
• Distributed mode, model loaded on exactly one worker: same flow redirects (replace history entry) to `/app/node-backend-logs//` with the `?from=` timestamp preserved so the deep-link scrolls to the right line.
• Distributed mode, model loaded on multiple workers: picker renders one row per hosting worker (node id, replica index, state); clicking a row opens that worker's logs page.
• Distributed mode, model not loaded anywhere: empty state appears with a link to the Nodes page.
• Distributed mode, nodes API partial failure: a single offline worker doesn't hide logs available on its peers (per-node fetch errors are tolerated).