Add ESLint rules for TypeScript strict typing

- Add @typescript-eslint/no-explicit-any (warn) to discourage 'any' type
- Add @typescript-eslint/consistent-type-assertions (warn) to discourage
  type assertions while allowing 'as const' and object literals as parameters
- Rules are scoped to .ts and .tsx files via overrides

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>