Enable pyright strict mode via pyrightconfig.json

[alirezabayatmk]

Follow-up from #25.

Current state

Pyright runs in default mode in CI and pre-commit. The codebase is clean under default mode but has not been validated against strict mode.

What this tracks

Enable strict-mode pyright per @reckart's original spec in #25. Full config JSON is in the body of #25.

Key flags:

• typeCheckingMode: strict
• include: src
• reportMissingTypeStubs, reportMissingImports, reportOptionalMemberAccess, reportPrivateUsage, reportUntypedFunctionDecorator, reportUntypedBaseClass, reportUnknownArgumentType, reportUnknownVariableType: true
• reportUnusedImport: warning

Approach

Expect strict mode to surface many new errors. Suggested rollout:

1. Drop pyrightconfig.json with strict enabled
2. Enumerate the error set
3. Fix what's worth fixing; selectively relax flags that aren't
4. Land as one or more focused PRs

Not 0.1.0-blocking: default-mode pyright is already a real check.