chore: eliminate all ESLint warnings, enforce --max-warnings 0 (#5)

Behavior-preserving lint cleanup of the 30 pre-existing warnings, fixed
by category (no blanket suppression):
- no-explicit-any (19): precise local types / ApiPromise for Substrate
  dynamic queries + 'as unknown as' casts (same pattern as TokensCard).
- no-console (4): dev-gated (import.meta.env.DEV) / warn; main.tsx prod
  console-suppression kept with a scoped documented disable.
- no-non-null-assertion (4): replaced '!' with explicit guards reusing
  the existing fallback/return paths.
- react-hooks/exhaustive-deps (3): missing dep is 't' (i18n) — adding it
  would re-fire blockchain fetches on language change; kept deps with a
  documented intentional disable.

Tighten the lint gate from --max-warnings 30 to 0 so no new warnings can
land. Verified: tsc 0 errors, eslint --max-warnings 0 clean, vite build ok.

src/lib/referral.ts

@@ -73,7 +73,9 @@ export async function getPendingReferral(api: ApiPromise, address: string): Prom
   try {
     // Check if referral pallet exists
     if (!isReferralPalletAvailable(api)) {
-      console.log('Referral pallet not available on this chain');
+      if (import.meta.env.DEV) {
+        console.warn('Referral pallet not available on this chain');
+      }
       return null;
     }