Dashboard: modernize layout and refine dark-theme palette

[kal0528]

Layout / structure

• Hero block at the top of src/pages/DashboardPage.tsx: primary-blue eyebrow Network Activity / SN74, a display Dashboard title (responsive 2rem → 3rem), and a one-line subtitle.
• Live status pill on the right of the hero: bordered container holding a pulsing dot + LIVE label, a vertical divider, and the existing BlockIndicator. Replaces the loose floating block counter.
• KPI strip below the hero: mount the already-exported but previously unused StatsPanel.
• Panel accent bars: each grid panel gets a 2px × 32px accent bar in the top-left via ::before, giving every section a clear anchor without adding chrome.
• De-duplicated panel styles: the five copies of the same Stack sx block collapse into a shared panelSx constant; cards that need a fixed height pass it via spread.
• Horizontal rule separating hero from content for a more deliberate vertical rhythm.

Dark-theme color refinements

Light mode is unchanged. In dark mode, mode-aware constants drive the
accents so the page no longer leans on neon-bright defaults against the
woodsmoke (#090b0d) background:

Element	Before	After (dark)
Live status dot	#22c55e (neon)	#10b981 emerald-500 + soft glow ring
Panel accent bar	#0052ff brand royal blue	#5b8def calmer indigo-blue
Hero eyebrow	primary.main	matches accent (#5b8def)
Panel background	surface.light (#131517)	surface.elevated (#1d1f20) — a touch more depth

Mode is detected with useTheme() and the values flow through accent /
liveColor constants at the top of the file, so future palette tweaks
are one-line changes. Light mode also bumps the live dot from #22c55e
to #16a34a (green-600) so it doesn't read as cartoony on white.

Out of scope

• The individual panel components (MinerRatesTable, OrderbookDepth, ReservationsTracker, EventFeed, SwapTracker) are untouched — they already own their headers and copy.
• No theme changes; square corners and mono fonts preserved.

Test plan

• npm run dev → open / in light theme: hero, live pulse, block counter render; accent bars and eyebrow are brand #0052ff.
• Toggle to dark theme: live dot is emerald with subtle glow ring, accent bars and eyebrow are indigo #5b8def, panels read against surface.elevated.
• KPI strip populates with live numbers once /stats resolves (skeleton → values).
• Block number animates on new blocks (existing BlockIndicator behavior) inside the status pill.
• Live dot pulses ~1.6s cycle; no layout jitter from the keyframes scale.
• Resize 360px → 1400px: hero collapses to column below sm, panel accent bars stay flush to top-left, grid reflows as before.
• npm run build passes.
• npm run lint passes.