docs: add WarpGrep example suite (10 examples)

Self-contained examples covering local search, GitHub search, streaming,
node_modules, and agent integrations (Anthropic, OpenAI, Vercel AI SDK,
Gemini, Python raw API). Literate // comment style throughout. Each
example has a unique default query and clear usage instructions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>