[opencode] Sprint 2: Config management + model list + health check

[SkyWalker2506]

Sprint 2 Tasks

• S2-T1: Create models.json — static list of Zen free models + popular Ollama models
• S2-T2: Add scripts/opencode-models.sh — reads models.json + runs ollama list, outputs combined table
• S2-T3: Create config/opencode-template.json — reference config shipped with plugin
• S2-T4: Update install.sh to copy template to ~/.config/opencode/opencode.json if missing
• S2-T5: Add scripts/opencode-health.sh — ping Zen API + check Ollama serve + verify config valid

Depends on: #2 (Sprint 1)
Priority: P1 high