chore(core): strict TS + typed ESLint

[morapay-app]

Summary

• Enforced TS strictness required by Enforce strict TypeScript compilation and linting #69 (strict, noImplicitAny, exactOptionalPropertyTypes).
• Configured type-aware ESLint (@typescript-eslint/strict-type-checked + @typescript-eslint/stylistic-type-checked) with a dedicated tsconfig.eslint.json and parserOptions.project.
• Unblocked CI by aligning the toolchain so installs/tests run deterministically (ts-jest currently requires TypeScript < 6, so the root TS devDependency is pinned to a compatible 5.9.x line).

Notes / rationale

• This PR includes follow-up fixes that became mandatory once strictness + typed linting were enabled (API surface mismatches, optional-property semantics, and monorepo typecheck ordering).

Acceptance criteria coverage

• TS config: strict, noImplicitAny, exactOptionalPropertyTypes enabled.
• ESLint: strict-type-checked + stylistic-type-checked enabled; parserOptions.project points to tsconfig.eslint.json.
• Lint/typecheck/tests run successfully.

Test plan

• npm install
• npm run typecheck
• npm run lint
• npm test

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Hey @morapay-app! 👋 It looks like this PR isn't linked to any issue.

If this PR is for one of the issues assigned to you as part of a Wave, please link it to ensure your contribution is tracked properly. You can do this by adding a keyword to the PR description (e.g., Closes #123), or by clicking a button below:

Issue	Title
#101	Implement Hardware Wallet Connector (Ledger/Trezor)	Link to this issue
#70	Setup size-limit to monitor bundle size	Link to this issue
#69	Enforce strict TypeScript compilation and linting	Link to this issue

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[AlAfiz]

@morapay-app please resolve conflicts and link issue to pr