feat(mermaid): comprehensive mermaid diagram rendering improvements

Complete overhaul of Mermaid diagram rendering system with fixes for
flowcharts, sequence diagrams, bar/XY charts, and mind maps.

Flowchart Rendering:
1. Intelligent edge routing with obstacle avoidance
   - Vertical alignment detection with offset L-shaped routing
   - Orthogonal routing for complex cases
   - Crossing minimization and coordinate optimization
2. Adaptive node spacing based on complexity
   - MermaidGraphAnalyzer calculates graph metrics
   - Dynamic width/height adjustments prevent overlaps
3. Fixed height clipping for large diagrams
4. Cycle and disconnected node handling

Sequence Diagrams:
- Fixed arrow syntax parsing by reordering pattern matching
- Check longer patterns first (-->> before ->>) to prevent
  substring false matches

Bar and XY Charts:
1. Added 'series' keyword support for data parsing
2. Implemented space-separated category parsing for x-axis
3. Auto-detection of format (values vs coordinate pairs)
4. Backward compatibility with legacy format

Mind Maps:
- Implemented indentation normalization to handle markdown
  code block indentation, enabling correct hierarchy parsing
  for full tree display

Files Changed:
- FlowchartRenderer.swift: Complete routing system overhaul
- MermaidGraphAnalyzer.swift: New graph analysis utilities
- MermaidParser.swift: Parser fixes for all diagram types
- MermaidDiagramView.swift: Integration improvements

Testing:
- All diagram types from mermaid.txt render correctly
- Flowchart edge routing handles complex topologies
- Sequence diagrams parse all arrow types
- Bar/XY charts display series data
- Mind maps show full hierarchy

Impact:
Mermaid diagrams now render reliably in SAM with proper layout,
routing, and data parsing across all supported diagram types.

Author: fewtarius