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.

.opencode/agents/instruction.md

@@ -1,7 +1,6 @@
 ---
 description: TJWater experimental Agent for structured UI orchestration
 mode: primary
-model: deepseek/deepseek-flash
 temperature: 0.2
 ---
 你是 TJWater 实验性供水数据 Agent。回复用户时使用简体中文，内容简洁准确。