add Plano agent skills framework and rule set (#797)

* feat: add initial documentation for Plano Agent Skills

* feat: readme with examples

* feat: add detailed skills documentation and examples for Plano

---------

Co-authored-by: Adil Hafeez <adil.hafeez@gmail.com>

skills/rules/config-providers.md

@@ -0,0 +1,64 @@
+---
+title: Register Model Providers with Correct Format Identifiers
+impact: CRITICAL
+impactDescription: Incorrect provider format causes request translation failures — Plano must know the wire format each provider expects
+tags: config, model-providers, llm, api-format
+---
+
+## Register Model Providers with Correct Format Identifiers
+
+Plano translates requests between its internal format and each provider's API. The `model` field uses `provider/model-name` syntax which determines both the upstream endpoint and the request/response translation layer. Some providers require an explicit `provider_interface` override.
+
+**Provider format reference:**
+
+| Model prefix | Wire format | Example |
+|---|---|---|
+| `openai/*` | OpenAI | `openai/gpt-4o` |
+| `anthropic/*` | Anthropic | `anthropic/claude-sonnet-4-20250514` |
+| `gemini/*` | Google Gemini | `gemini/gemini-2.0-flash` |
+| `mistral/*` | Mistral | `mistral/mistral-large-latest` |
+| `groq/*` | Groq | `groq/llama-3.3-70b-versatile` |
+| `deepseek/*` | DeepSeek | `deepseek/deepseek-chat` |
+| `xai/*` | Grok (OpenAI-compat) | `xai/grok-2` |
+| `together_ai/*` | Together.ai | `together_ai/meta-llama/Llama-3` |
+| `custom/*` | Requires `provider_interface` | `custom/my-local-model` |
+
+**Incorrect (missing provider prefix, ambiguous format):**
+
+```yaml
+model_providers:
+  - model: gpt-4o            # Missing openai/ prefix — Plano cannot route this
+    access_key: $OPENAI_API_KEY
+
+  - model: claude-3-5-sonnet # Missing anthropic/ prefix
+    access_key: $ANTHROPIC_API_KEY
+```
+
+**Correct (explicit provider prefixes):**
+
+```yaml
+model_providers:
+  - model: openai/gpt-4o
+    access_key: $OPENAI_API_KEY
+    default: true
+
+  - model: anthropic/claude-sonnet-4-20250514
+    access_key: $ANTHROPIC_API_KEY
+
+  - model: gemini/gemini-2.0-flash
+    access_key: $GOOGLE_API_KEY
+```
+
+**For local or self-hosted models (Ollama, LiteLLM, vLLM):**
+
+```yaml
+model_providers:
+  - model: custom/llama3
+    base_url: http://host.docker.internal:11434/v1   # Ollama endpoint
+    provider_interface: openai                        # Ollama speaks OpenAI format
+    default: true
+```
+
+Always set `default: true` on exactly one provider per listener so Plano has a fallback when routing preferences do not match.
+
+Reference: https://github.com/katanemo/archgw