feat(dashboard): added bandwidth graph

[Je3r]

Fix #5152

Added a graph showing the last minute of upload and download bandwidth in the dashboard.

The code was written by GPT 5.6 Sol (Codex)

[CLAassistant]

All committers have signed the CLA.

[github-actions]

Rule Review: No issues found

Rules checked: git-workflow.md, code-style.md, testing.md
Files reviewed: 6

The Rust-side change is a small, additive format! extension in cards.rs (numeric fields only, no injection risk) plus one new regression-style test in home_page.rs — neither triggers any of the applicable code-style.md patterns (no .unwrap() in production code, no spawns, no retry loops, no biased;, no time/rng/socket usage, no persisted config fields). The bulk of the change is browser-side JavaScript (dashboard.js, bandwidth_chart.test.mjs) and CSS, which fall outside the Rust-scoped code-style.md (**/*.rs) and outside the Rust-specific concerns of testing.md (TimeSource/GlobalRng/SimulationSocket). The new .mjs test suite is unusually thorough for the areas testing.md's "edge cases and boundary conditions" section calls out — zero/negative/invalid counters, BigInt overflow, backward clocks, counter resets, window gaps, empty/partial history, and viewport-edge tooltip clamping are all covered. The commit message follows conventional-commits format. No PR-description content was available to review that section of git-workflow.md.

No rule violations detected.

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Rule review against .claude/rules/. WARNING findings block merge.