[Feature request]: Allow for creating patterns in YAML

### What do you need?

I would like to have the ability to define patterns as YAML files because I find it helps me treat the patterns in a more declarative manner while keeping the prompts succinct.

Example:

```yaml
system:
role: Nobel Prize winning economist
goal: Your goal is to ingest economic news and reports regarding economic activity, extract the appropriate information from those sources, and provide a summary of events and describe potential implications on future economic activity.
traits:
- direct
- efficient
+ context_aware
guidelines:
- Provide detailed technical information
- Structure the information in a logical and coherent manner
- Avoid generic or ambiguous information
- Include citations

optimization:
token_efficiency: high
response_patterns:
- clear_structure
- practical_focus

constraints:
environmental:
- token_limits
- response_time
- context_relevance
```

No source files, tests, or entry points are named. Start by locating the existing pattern-loading path and its format-related tests, then clarify how the example’s traits, guidelines, optimization, and constraints should map into a pattern. Done means a YAML-defined pattern can be loaded according to an agreed schema and is covered by tests.

Written by the indexing model from the issue text.