fix: fullscreen diagram export background color mismatch

Use the same isDark value from Mermaid render time instead of
re-checking CSS variables. Fixes white-on-white text when
exporting dark-mode diagrams.

feat: add install-pi.sh for one-command Pi installation

Patches {{skill_dir}} to actual path at install time. Simplifies README
install instructions.

feat: multi-diagram support with vector-based zoom/pan engine

Replace CSS zoom with direct SVG sizing. Closure-based initDiagram() pattern
supports unlimited diagrams per page with no ID collisions. Includes adaptive
viewport height, smart fit algorithm, touch pinch-to-zoom, and double-click
to fit.

Co-authored-by: David Abraham <dave@springbasemedia.com>

chore: bump version to 0.5.1

- Update CHANGELOG with marketplace structure and Pi manual install changes
- Fix misleading 'marketplace' descriptions in plugin metadata
- Bump version in package.json and all plugin.json files

docs: update changelog for v0.5.0

feat: hybrid architecture pattern for complex diagrams

- New pattern for 15+ elements: simple Mermaid overview + CSS Grid cards
- Reduced max Mermaid nodes from 15-20 to 10-12
- Updated scaling guidance to recommend hybrid over scaling tricks

chore: bump version to 0.4.3

fix: add link styling guidance to prevent low-contrast links

feat: v0.4.1 — Mermaid TD vs LR guidance, README simplification

Mermaid layout direction:
- New 'Layout Direction: TD vs LR' section in libraries.md
- Prefer flowchart TD over LR for complex diagrams (5+ nodes)
- Updated all diagram type sections to recommend TD first

Documentation:
- Simplified README: consolidated Install, added Slide Deck Mode section
- Added /generate-visual-plan to command table

feat: v0.4.0 — /generate-visual-plan, prose accents, mermaid fixes

New prompt template:
- /generate-visual-plan for context-first feature specs with state machines,
  before/after panels, edge case tables, and implementation notes

New patterns:
- Prose accents: lead paragraphs, pull quotes, callouts, theme toggle
- Code blocks: whitespace preservation, file headers
- Documentation mapping: features→cards, steps→flows, APIs→tables

Mermaid fixes:
- Centering for narrow vertical flowcharts
- Scaling guidance for complex diagrams (fontSize 18-20px)
- Special character escaping in node labels

Bug fixes:
- List marker overflow in bordered containers
- Code block whitespace preservation