SPRINT #2 ISSUE 5: Core functionality restoration - implement missing APIs preventing user workflow completion

[krystophny]

SCOPE: Implement critical missing functionality blocking user workflow completion identified in PLAY audit

MISSING FUNCTIONALITY IMPLEMENTATION:

• Implement colorbar function promised in documentation but not existing (CRITICAL: Colorbar function not implemented despite documentation promises #752)
• Fix text annotation system falsely advertised as working (CRITICAL USER DECEPTION: Text annotation example falsely advertises non-existent functionality #785)
• Restore PDF file writing system functionality (CRITICAL: PDF file writing system failure blocks core functionality #696)
• Fix core user workflows broken by reorganization (USER ACCEPTANCE TEST FINDINGS: Multiple core workflows broken after sprint reorganization #799)

SUCCESS CRITERIA:

• Colorbar function: Fully functional with all documented parameters
• Text annotation: Complete implementation matching documentation promises
• PDF output: Reliable file generation for all plot types
• Core workflows: All documented user workflows complete successfully

VERIFICATION:

• Colorbar examples → generate correct visual outputs
• Text annotation examples → render text as documented
• PDF generation → creates valid PDF files for all plot types
• User acceptance tests → all core workflows pass

USER IMPACT:
Restores promised functionality preventing user abandonment due to broken workflows

REFERENCES: Consolidates issues #696, #752, #785, #799

[krystophny]

Closing sprint epic; shift to actionable, scoped issues only.