feat(admin): add price oracle approved callers panel (#829)

[Seunfunmi-319509]

Summary

Closes #829

Adds an Oracle Access panel to a new Admin Dashboard (/admin/dashboard) so admins can manage the external contract addresses permitted to call the AccessLayer price oracle. Previously this list had no admin UI.

What's included

• New Admin Dashboard route — src/pages/AdminDashboardPage.tsx registered at /admin/dashboard in src/routes.tsx. (No admin dashboard existed in the client yet, so this PR introduces the page and the Oracle Access section as its first panel.)
• Oracle Access panel — src/components/admin/OracleAccessPanel.tsx:
  • Lists approved callers fetched from GET /admin/oracle/callers, each with a Remove button.
  • Add input + Add button that submits via POST /admin/oracle/callers and refreshes the list.
  • Validation: the Add button stays disabled until the input is a valid Stellar contract address (56-char C-prefixed strkey, valid base32 + CRC16-XModem checksum). Invalid input shows inline validation, and duplicates already in the list are rejected.
  • Confirmation dialog before removing a caller (DELETE /admin/oracle/callers/:address).
  • Empty state when no callers are approved, loading skeleton, and load-error/retry state.
• API layer — src/services/admin.service.ts (AdminService extending BaseApiService) with getOracleCallers, addOracleCaller, removeOracleCaller, plus test-friendly wrapper functions.
• Hooks — src/hooks/useOracleCallers.ts (useOracleCallers, useAddOracleCaller, useRemoveOracleCaller) with React Query cache invalidation and success/error toasts.
• Validation util — src/utils/stellarAddress.utils.ts implementing proper strkey checksum validation (base32 decode + CRC16-XModem), not just regex length checks.
• Query key — admin.oracleCallers added to src/lib/queryKeys.ts.

Acceptance criteria

• Approved callers listed with Remove button per entry
• Invalid contract address shows validation error (gated Add button + inline error)
• Add button submits the new caller and updates the list (invalidates the query)
• Remove button removes the caller after confirmation
• Empty state shown when no callers are approved

Testing

• pnpm lint — passes
• pnpm build — passes (tsc -b && vite build)

New unit tests (33 assertions, all passing):

• src/utils/__tests__/stellarAddress.utils.test.ts — valid/invalid/checksum-tampered/lowercase/format cases.
• src/services/__tests__/admin.service.test.ts — GET normalization, POST/DELETE payloads, error mapping.
• src/components/admin/__tests__/OracleAccessPanel.test.tsx — listing, empty state, loading, validation gating, add flow, remove-after-confirmation, cancel.

Notes / assumptions

• The issue specifies only GET/POST /admin/oracle/callers. Remove is implemented as DELETE /admin/oracle/callers/:address (RESTful, matches the existing route prefix); the server module isn't in accesslayer-server yet, so the client-side contract is documented here for coordination.
• The read endpoint is intentionally lenient: it accepts [{ address }], plain string arrays, or a { callers: [...] } envelope so it works regardless of the exact server shape.

Checklist

• Linked issue or backlog item (Add a price oracle approved callers panel on the admin dashboard to manage external contract integrations #829)
• Scope is limited to the stated change
• Updated docs if behavior or setup changed
• Added screenshots for UI changes when relevant

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