Publish durable settlement launch posts

[amavashev]

What changed

• add a featured release story, “The Model Call Succeeded. Then the Process Died,” explaining the known-spend failure boundary and fleet-wide durable recovery contract
• add a code-first “Durable Budget Control for LangChain Agents” tutorial covering model, tool, and fan-out gates, actual/cache-aware usage, settlement surfacing, streaming boundaries, and failure testing
• connect both posts to the existing critical-path benchmark article, SDK recovery conformance matrix, durability contract, current releases, and upstream LangChain middleware listing

Why

The 0.5.3/0.4.3/0.3.3 SDK releases and langchain-runcycles 0.4.0 shipped one reliability story across several repositories. These posts give the release a customer-visible failure narrative and an immediate adoption path without duplicating the existing engineering proof article.

The homepage, install-count cache, and generated assets are intentionally unchanged.

Verification

• npm test — 103 tests passed
• npm run build — OpenAPI conversion, LLM corpus, two OG cards, VitePress site, sitemap/RSS, and PDFs passed
• featured launch PDF rendered successfully
• both generated HTML routes exist
• every internal link in the two posts resolves to a source page
• Python example parses successfully
• git diff --check clean