feat(agents): add model selection and standardize frontmatter

Add per-agent model selection using Claude Code's now-supported `model`
frontmatter field, and standardize all agent frontmatter across the
marketplace.

Changes:
- Add `model` field to all 25 agents (18 sonnet, 7 haiku)
- Fix viz-platform/data-platform agents using `agent:` instead of `name:`
- Remove non-standard `triggers:` field from domain agents
- Add missing frontmatter to 13 agents
- Document model selection in CLAUDE.md and CONFIGURATION.md
- Fix undocumented commands in README.md

Model assignments based on reasoning depth, tool complexity, and latency:
- sonnet: Planner, Orchestrator, Executor, Coordinator, Security Reviewers
- haiku: Maintainability Auditor, Test Validator, Git Assistant, etc.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/viz-platform/agents/component-check.md

@@ -1,6 +1,7 @@
 ---
 name: component-check
 description: DMC component validation specialist
+model: haiku
 ---
 
 # Component Check Agent

plugins/viz-platform/agents/design-reviewer.md

@@ -1,10 +1,7 @@
 ---
-agent: design-reviewer
-description: Reviews code for design system compliance using viz-platform MCP tools
-triggers:
-  - /design-review command
-  - /design-gate command
-  - projman orchestrator domain gate
+name: design-reviewer
+description: Reviews code for design system compliance using viz-platform MCP tools. Use when validating DMC components, theme tokens, or accessibility standards.
+model: sonnet
 ---
 
 # Design Reviewer Agent

plugins/viz-platform/agents/layout-builder.md

@@ -1,3 +1,9 @@
+---
+name: layout-builder
+description: Practical dashboard layout specialist for creating well-structured layouts with filtering, grid systems, and responsive design.
+model: sonnet
+---
+
 # Layout Builder Agent
 
 You are a practical dashboard layout specialist. Your role is to help users create well-structured dashboard layouts with proper filtering, grid systems, and responsive design.

plugins/viz-platform/agents/theme-setup.md

@@ -1,3 +1,9 @@
+---
+name: theme-setup
+description: Design-focused theme setup specialist for creating consistent, brand-aligned themes for Dash Mantine Components applications.
+model: haiku
+---
+
 # Theme Setup Agent
 
 You are a design-focused theme setup specialist. Your role is to help users create consistent, brand-aligned themes for their Dash Mantine Components applications.