docs: quickstart guide with interactive LLM and project structure

[anistark]

Changes Made

Documentation (docs/getstarted/evals.md):

• Added quickstart cmd to follow through guide with an example project.
• Updated "Custom Evaluation with LLMs" to reference DiscreteMetric from
  generated code
• Replaced static examples with modern llm_factory API
• Changed "Using Pre-Built Metrics" to AspectCritic with modern async/await
  syntax
• Updated "Evaluating on a Dataset" to use ragas.Dataset API

Build Configuration (mkdocs.yml):

• Made social plugin conditional: enabled: !ENV [MKDOCS_CI, true]

Makefile:

• Added explicit MKDOCS_CI=false to serve-docs target. This avoids social plugin error in macos if in case cairosvg is not found.