feat(agent): unify models and validate OpenCode providers

Generate chat, task and learning models from agent-models.json.
Use WaterNetwork fast/expert models with 272k context and validate
upstream names before readiness. Add an isolated model check command
with signal-safe cleanup and plugin, Skill and MCP management docs.

Verified in isolation: type checks, 26 focused tests and both model
catalog checks; no model inference requests.

.gitignore

@@ -3,6 +3,7 @@ __pycache__/
 .opencode/node_modules/
 .opencode/skills/
 .local.env
+agent-models.local.json
 .vscode
 docker-compose.yml
 data/