Fix the casing of "PyPI" across docs and integration pages. The Python
Package Index spells it "PyPI" (capital P-y-capital-P-capital-I), but
several pages used "PyPi" instead.
Document the `AGENTS.md` file-based approach for defining custom
subagents in the Deep Agents CLI. CLI users can now define subagents as
markdown files with YAML frontmatter instead of writing them in code,
and optionally override the model per subagent for cost control.
## Description
Adds Vale terminology rules to enforce correct capitalization of "Deep
Agents". Catches common incorrect variants (`deep agents`, `Deep
agents`, `DeepAgents`, `deepagents`) and suggests the correct form.
Resolves DOC-859
## Test Plan
- [ ] Run `vale --config .vale.ini` against a test file with incorrect
variants to verify all four patterns are caught
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Co-authored-by: open-swe[bot] <open-swe@users.noreply.github.com>
Co-authored-by: Lauren Hirata Singh <lauren@langchain.dev>
Mason Daugherty