fix(core): DuplicateDMLOperation handles JSON-sourced boolean flow metadata

[RubenHalman]

Summary

• DuplicateDMLOperation compared allowBack/showFooter strictly against the string "true", so flows built from Tooling API JSON (real booleans, e.g. the Salesforce app fetching Flow.Metadata) never matched: violations went unreported and the back-disabled reset never fired.
• Added a small isTrue helper (matches the coercion pattern already used in MissingNullHandler.ts and RecordIdAsString.ts) and used it in all three comparisons.

Impact

Any consumer that hands core Tooling API JSON instead of parsed XML is affected, including Salesforce Inspector Reloaded and Org Check, as well as the LFS Salesforce app. On those, this rule silently reports nothing on screens with back navigation, and the reset fires on every screen.

Scope note

Evaluated the "coerce booleans once at Flow construction" structural alternative suggested on the ticket. Decided against it for this fix: it would touch shared Flow/FlowNode parsing broadly for every rule, which is a bigger blast radius than this scoped bug warrants. The local isTrue helper matches the existing per-rule pattern and is the minimal correct fix.

Rollout to force-app/main/default/staticresources/LFS_Core.js in the LFS Salesforce app repo is a separate follow-up once this lands in a core release — not bundled into an unreleased build here.

Test plan

• New regression test: JSON-shaped flow (real booleans) reports the violation
• New regression test: JSON-shaped flow verifies the back-disabled reset clears the seen-DML flag
• Existing XML-based tests still pass
• npx jest — full core suite green except pre-existing, unrelated SanityTest.test.ts UMD-global failure (confirmed present on main before this change, needs a UMD build artifact)
• tsc --noEmit clean

Plane: LFS-15