Type safety: eliminate all `any` types across codebase

[satsdisco]

Summary

ESLint reports 45+ no-explicit-any errors scattered across the codebase. The worst offenders:

• useNostr.ts — 17 instances (NDK signer wrappers, catch blocks, event types)
• App.tsx — 5 instances (AppRoutes props, event handlers)
• signer.ts — typed loosely
• nostr.ts — event building/publishing
• androidSigner.ts — intent handling
• upload.ts — response handling
• Various catch blocks using catch (e: any) instead of unknown

Approach

1. Define proper interfaces for Nostr events, NDK signers, relay results
2. Use nostr-tools built-in types where available
3. Replace catch (e: any) with catch (e: unknown) + type narrowing
4. Create a types/ directory with shared interfaces if needed
5. Extend src/types/nostr.ts with missing types

Acceptance Criteria

• Zero @typescript-eslint/no-explicit-any errors
• No loss of functionality
• Build passes cleanly