Migrate gittensory-miner-ui onto the shared design system

[JSONbored]

Problem: Once a shared design-system package exists, apps/gittensory-miner-ui's routes (index.tsx, portfolio.tsx, run-history.tsx) still use ad hoc hardcoded Tailwind classes (border-white/10, bg-white/5, text-white/70) with no relationship to the main site's actual tokens or components, and support only a forced dark theme with no light-mode toggle at all.

Area: Design system / Miner UI

Proposal: Replace gittensory-miner-ui's current 17-line stylesheet with the shared design-system package's tokens, and rewrite its route markup to use the shared component primitives (Card, Badge, Table, Button, etc.) instead of raw hardcoded utility classes — bringing it to genuine visual and structural parity with the main site.

Deliverables:

• gittensory-miner-ui depends on and renders through the shared design-system package.
• Every existing route (Overview, portfolio, run-history) rebuilt using the shared component primitives.
• Full light + dark theme support, matching the main site's toggle behavior (today it's dark-only).

Acceptance criteria:

• Side-by-side visual review confirms gittensory-miner-ui is consistent with gittensory-ui — same fonts, colors, spacing, component styling, in both themes.
• No hardcoded colors or fonts remain anywhere in gittensory-miner-ui's own code — everything routes through the shared package's tokens.

Test scenarios:

• Screenshot comparison of each miner-ui route against an equivalent gittensory-ui page, light and dark.
• Toggle between themes and confirm every route renders correctly in both.

Resources:

• apps/gittensory-miner-ui/src/routes/{index,portfolio,run-history}.tsx (current ad hoc markup to replace).
• The shared design-system package from the companion extraction issue.

Boundaries:

• Depends on the design-system-package extraction issue landing first — don't duplicate tokens/components locally as a stopgap.

[linear-code]

JSO-3608