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>

CHANGELOG.md

@@ -58,6 +58,31 @@ New scripts for installing marketplace plugins into consumer projects:
 - `viz-platform` → `["viz-platform"]`
 - `contract-validator` → `["contract-validator"]`
 
+#### Agent Model Selection
+
+Per-agent model selection using Claude Code's now-supported `model` frontmatter field.
+
+- All 25 marketplace agents assigned appropriate model (`sonnet`, `haiku`, or `inherit`)
+- Model assignment based on reasoning depth, tool complexity, and latency requirements
+- Documentation added to `CLAUDE.md` and `docs/CONFIGURATION.md`
+
+**Supported values:** `sonnet` (default), `opus`, `haiku`, `inherit`
+
+**Model assignments:**
+| Model | Agent Types |
+|-------|-------------|
+| sonnet | Planner, Orchestrator, Executor, Code Reviewer, Coordinator, Security Reviewers, Data Advisor, Design Reviewer, etc. |
+| haiku | Maintainability Auditor, Test Validator, Component Check, Theme Setup, Git Assistant, Data Ingestion, Agent Check |
+
+### Fixed
+
+#### Agent Frontmatter Standardization
+
+- Fixed viz-platform and data-platform agents using non-standard `agent:` field (now `name:`)
+- Removed non-standard `triggers:` field from domain agents (trigger info already in agent body)
+- Added missing frontmatter to 13 agents across pr-review, viz-platform, contract-validator, clarity-assist, git-flow, doc-guardian, code-sentinel, cmdb-assistant, and data-platform
+- All 25 agents now have consistent `name`, `description`, and `model` fields
+
 ---
 
 ## [5.8.0] - 2026-02-02