docs: fix TypeScript table count return type

[clockwork-labs-bot]

Summary

• Update the TypeScript client reference so TableHandle.count() returns bigint, matching crates/bindings-typescript/src/lib/table.ts and existing TypeScript SDK tests.
• Clarify spacetime publish environment behavior: ordinary publishes preserve unspecified stored values by default, and optional values are removed only through explicit unset or replacement.

Audit notes

• Required PR preflight found open bot/docs-audit PR docs: fix TypeScript table count return type #5936, so this run updated the existing PR branch.
• Merged current origin/master into bot/docs-audit before adding today's audit fix.
• Commit-impact pass: source PR Implement persistent typed database environments #5887 introduced persistent typed database environments. The docs fix aligns the publish concept page with the new CLI reference, environment variables guide, implementation, and smoketests.
• Compared current skill files in skills/*/SKILL.md against public docs for CLI flows, SDK APIs, server module APIs, auth, onboarding, deployment, MCP, and cross-language casing consistency.

Validation

• pnpm build in docs/ passed. It emitted the existing docusaurus-plugin-llms-txt warning for /docs/ask-ai/ask-ai, then generated static files successfully.