fix(appsync): remove optional chaining from JS 1.0.0 resolvers

[dmeiser]

AppSync JS runtime 1.0.0 does not support ES2020 optional chaining (?.). Replaced ?. with explicit null checks in three resolver files to prevent runtime parse/execution errors.

• ensure_my_account_exists_fn.js
• check_existing_share_fn.js
• list_my_shares_resolver.js

Validation: node --check on all JS resolver files; tofu validate in tofu/application/environments/dev passes (pre-existing hash_key deprecation warnings remain).

[Copilot]

Pull request overview

This PR updates AppSync JavaScript (runtime 1.0.0) resolvers to avoid ES2020 optional chaining (?.), replacing it with explicit null checks to prevent resolver parse/execution failures in the AppSync runtime.

Changes:

• Replaced ctx.result?.items with an explicit ctx.result && ctx.result.items guard in listMyShares response handling.
• Replaced optional-chained Cognito claim access with explicit ctx.identity / claims checks in account bootstrap logic.
• Replaced optional-chained stash invite access with an explicit ctx.stash.invite presence check when selecting profileId.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
tofu/application/appsync/js-resolvers/list_my_shares_resolver.js	Removes optional chaining when reading ctx.result.items to keep the resolver compatible with AppSync JS 1.0.0.
tofu/application/appsync/js-resolvers/ensure_my_account_exists_fn.js	Removes optional chaining from identity claim lookup to prevent runtime syntax errors in AppSync JS 1.0.0.
tofu/application/appsync/js-resolvers/check_existing_share_fn.js	Removes optional chaining from ctx.stash.invite access to avoid unsupported syntax in AppSync JS 1.0.0.