frontend: Use linux2rest network probe deltas for tray rates

[joaoantoniocardoso]

Summary

• Derive tray upload/download speeds from linux2rest received_B / transmitted_B (sysinfo per-sample deltas) divided by the Sampler interval (5s), instead of re-differencing total_* across frontend polls.
• That removes negative Mbps when totals reset and avoids flicker/spikes against the ≥0.9 sample cache.
• NetworkCard now shows probe deltas alongside totals (same shape as linux2rest's own UI).
• Also fixes the transmitted_B type docstring (was copy-pasted as "bytes received"), swaps the swapped mdi-cloud-upload/mdi-cloud-download icons on the byte rows, and rewords labels to Packets received/transmitted.

Closes #3587

Note: The target is BlueOS 1.5 only.

Test plan

• Against BlueOS with linux2rest 0.9.x: enable eth0 Networking widget under steady traffic
• Rate stays stable across 2s polls within a 5s sample window (no flicker to 0)
• Rate updates when the Sampler advances; never goes negative
• System Information → Network cards show delta / total for packets and bytes
• Byte-row icons match direction (download on received, upload on transmitted)

[github-actions]

Automated PR Review

0. Summary

• Verdict: LGTM

Switches the Networking widget's upload/download rates from a frontend re-diff of total_*_B counters to the per-sample received_B / transmitted_B deltas exposed by linux2rest, dividing by the (hardcoded, documented) 5s Sampler interval. This eliminates the negative-Mbps window during counter resets and the flicker/zeroing that occurred whenever the 2s frontend poll landed inside the same 5s linux2rest sample cache. Also drops the now-unused Network.last_update field, corrects the transmitted_B JSDoc (was copy-pasted as "bytes received"), swaps the inverted mdi-cloud-upload / mdi-cloud-download icons on the byte rows in NetworkCard.vue, and adds the per-sample delta alongside the running total.

No further comments, nice job 👍

Generated by PR Review Bot. This is advisory, a human reviewer must still approve.

[joaoantoniocardoso]

Addressed from the latest review:

• Clamp at source in networkProbeRateBps (formatter stays pure)
• camelCase bytesSinceLastProbe
• Consistent NetworkCard labels (Packets received/transmitted)

Deferred / intentional:

• Hardcoded 5 s Sampler interval → follow-up (expose from linux2rest or derive from unix_time_seconds)
• First-sample 0.00Mbps until the first non-zero delta window is intentional
• Disk-rate unification out of scope here