Align data model docs with actual ReconciliationPolicy API

[Copilot]

The data model documentation described a MergeStrategy type combining labels, properties, and elements into a single record, but the implementation uses separate ElementMergeStrategy and SubjectMergeStrategy types with a parameterized ReconciliationPolicy s.

Changes

• Type definitions: Updated ReconciliationPolicy from simple ADT to ReconciliationPolicy s with Merge constructor taking ElementMergeStrategy and value-specific strategy s
• Split strategy types: Replaced unified MergeStrategy with:
  • ElementMergeStrategy for element list merging (ReplaceElements | AppendElements | UnionElements)
  • SubjectMergeStrategy for Subject content with labelMerge and propertyMerge fields
• Default strategy: Updated defaultMergeStrategy references to defaultSubjectMergeStrategy
• Code examples: Updated quickstart.md examples to reflect actual API usage

Example

Before (documented but not implemented):

let strategy = MergeStrategy UnionLabels ShallowMerge UnionElements
reconcile (Merge strategy) pattern

After (actual implementation):

let subjectStrategy = SubjectMergeStrategy UnionLabels ShallowMerge
reconcile (Merge UnionElements subjectStrategy) pattern
-- Or use default: Merge UnionElements defaultSubjectMergeStrategy

Updated files: data-model.md, quickstart.md, research.md, spec.md, tasks.md

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[akollegger]

This is the wrong direction for a fix.