hotfix: align public documentation with v0.4.0

[manavanandani]

Summary

• update installation commands and release references to v0.4.0
• document the async agent lifecycle and RPC timeout controls available in the release
• remove documentation for pytest fixtures, dataset loading, and LangSmith export that is not present in the released packages

Root cause

The website content had moved ahead of the package release, while version references were not synchronized after v0.4.0 was published.

Validation

• local production-mode build (VERCEL=1 bun run build) completed successfully
• installed ecp-runtime==0.4.0 and ecp-sdk==0.4.0 from PyPI and verified timeout support for ecp run and ecp conformance
• executed the documented async manifest successfully: 3/3 scenarios passed
• targeted ESLint and source-content audits passed
• affected pages were inspected at desktop and mobile sizes with no browser errors

Baseline

Repository-wide lint continues to report existing formatting violations in untouched files; this hotfix introduces no additional lint violations.

[vercel]

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