Add TypeScript AppHost support to PostgreSQL integration docs

[davidfowl]

Add TypeScript AppHost support to the PostgreSQL integration documentation.

Cherry-picked from ts-integrations branch (replaces #581, rebased onto main).

[Copilot]

Pull request overview

This PR updates the PostgreSQL integration documentation to include TypeScript AppHost examples, adds a language-neutral “Connect to PostgreSQL” reference page, and introduces UI plumbing to keep language selectors/tabs in sync.

Changes:

• Add synced C#/TypeScript examples across the PostgreSQL hosting docs and restructure the PostgreSQL “get started” guide around AppHost language.
• Introduce a new “Connect to PostgreSQL” page with cross-language connection guidance, and update .NET client docs to point to it.
• Add a new SyncedPivotSelector component and a sidebar fix to keep the active page’s group expanded.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
src/frontend/src/content/docs/integrations/databases/postgres/postgres-host.mdx	Adds synced C#/TS hosting examples and updates guidance/links.
src/frontend/src/content/docs/integrations/databases/postgres/postgres-get-started.mdx	Splits quickstart by AppHost language; adds consumer-language tabs.
src/frontend/src/content/docs/integrations/databases/postgres/postgres-connect.mdx	New cross-language connection/environment-variable reference page.
src/frontend/src/content/docs/integrations/databases/postgres/postgres-client.mdx	Reframes as .NET-only client integration and links to connect page.
src/frontend/src/components/starlight/Sidebar.astro	Adds logic intended to expand the current page’s sidebar group.
src/frontend/src/components/SyncedPivotSelector.astro	New component to sync PivotSelector state with Starlight synced tabs.
src/frontend/config/sidebar/integrations.topics.ts	Adds sidebar entry for “Connect to PostgreSQL” and renames client entry.

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[eerhardt]

Should we rename this file because it is explicitly for .NET

[davidfowl]

Good call — will do this in a follow-up PR since renaming changes the URL slug and needs a redirect.

[eerhardt]

Why this one and not https://github.com/lib/pq?

[davidfowl]

Added a note explaining pgx is recommended for new projects (better performance, native protocol support, active maintenance) with a link to lib/pq as an alternative.

[eerhardt]

(nit) this looks different than the way we say to add the package to the app. Here:

Lower in the page it is a selector:

[davidfowl]

Leaving as-is — hosting and client packages have genuinely different install flows (aspire add vs dotnet add package), so the different UX is expected.

[IEvangelist]

This feels broader than needed for adding TypeScript AppHost coverage to the PostgreSQL docs. I'd prefer to keep this PR focused on the docs changes, reuse the existing PivotSelector/Pivot pattern with one shared key across the Postgres articles so the AppHost choice persists, and split the unrelated sidebar behavior change into a separate PR. If we keep or add an in-page PivotSelector, please use marginTop={1} so the spacing matches the rest of the docs. For language examples, let's also make sure we're covering the canonical popular/actively maintained OSS clients, or explicitly explain why we're choosing one over another.

[davidfowl]

@IEvangelist As we roll out TypeScript AppHost support to more integrations (Redis, MySQL, MongoDB, etc.), I'm noticing some patterns repeating across the Postgres pages that could be extracted into reusable components:

1. AppHostLanguageSwitcher — standardize the PivotSelector + key + "Select your AppHost language" boilerplate that every integration page will need
2. ClientLanguageTabs — the "install driver → import → read env vars → connect" pattern for JS/Python/Go/.NET that repeats across get-started and connect pages
3. ConnectionPropertyTable — env var property tables (Host, Port, Username, Password, Uri, etc.) that will repeat for every database integration

Postgres is the first integration with the C#/TS AppHost pivot, so it's a good time to extract these before we repeat the same patterns everywhere else. Do you agree this is worth doing, or should we keep things inline for now?