chore(docs-gen): harden XAML activity docs extraction and validation gates

[AlexMarinescuUiPath]

Summary
This change hardens the activity-doc-generator workflow to prevent repeated documentation defects seen in recent review cycles across docs PRs 525-530.

Root causes addressed

• Metadata parser assumed one JSON key casing.
• Property parser missed some accessor forms and fell back to weak typing.
• Internal infra properties could leak through merge paths.
• Required flags could be simultaneously true for one-of input pairs.
• Template could render noisy empty sections.
• No deterministic validation gate existed before review.

What changed

• Extraction parser now accepts both key casing styles.
• Property extraction now handles expression-bodied accessor patterns.
• Type merge prefers ViewModel type when activity type resolves as object.
• Internal property filtering is applied consistently.
• Requiredness normalization is applied to known one-of pairs and overload groups.
• Template sections are conditional on available rows.
• Skill now mandates strict validation before completion.
• New validator script enforces recurring defect classes.

Validation evidence

• Extractor run confirms expected activity discovery in Cryptography.
• Validator run catches known malformed XML fence patterns in sample markdown.
• Python syntax checks pass for changed and new scripts.

Risk and rollback

• Risk is low and localized to docs-generation workflow files.
• Rollback path is straightforward by reverting changed skill/template/scripts in this branch.

[sonarqubecloud]

Quality Gate failed

Failed conditions
1 Security Hotspot

See analysis details on SonarQube Cloud