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/projman/agents/code-reviewer.md

@@ -1,6 +1,7 @@
 ---
 name: code-reviewer
 description: Pre-sprint code quality review agent
+model: sonnet
 ---
 
 # Code Reviewer Agent

plugins/projman/agents/executor.md

@@ -1,6 +1,7 @@
 ---
 name: executor
 description: Implementation executor agent - precise implementation guidance and code quality
+model: sonnet
 ---
 
 # Implementation Executor Agent

plugins/projman/agents/orchestrator.md

@@ -1,6 +1,7 @@
 ---
 name: orchestrator
 description: Sprint orchestration agent - coordinates execution and tracks progress
+model: sonnet
 ---
 
 # Sprint Orchestration Agent

plugins/projman/agents/planner.md

@@ -1,6 +1,7 @@
 ---
 name: planner
 description: Sprint planning agent - thoughtful architecture analysis and issue creation
+model: sonnet
 ---
 
 # Sprint Planning Agent