Cross-reference TurboDocx Quickstart skill from SDK docs pages

Why

The TurboDocx Quickstart skill is an Agent Skills plugin that detects a user's project language and scaffolds working TurboDocx integration code (TurboSign, Deliverable, TurboPartner — and now TurboWebhooks for PHP, with other languages rolling in). It's the fastest way for an AI-assisted developer to go from "empty project" to "signature webhook receiver wired up."

Today the docs site doesn't surface it. A developer reading `/docs/SDKs/php` or `/docs/SDKs/webhooks-php` has no idea they could invoke a slash command in Claude Code / Cursor / Copilot to have the integration auto-installed.

We should cross-reference the Quickstart skill from every SDK reference page so AI-assisted users find it.

Scope

Add a short callout (admonition) to each of these pages:

• `docs/SDKs/index.md` — Overview page; top-of-page callout
• `docs/SDKs/javascript.md` (TurboSign JS)
• `docs/SDKs/python.md` (TurboSign Python)
• `docs/SDKs/php.md` (TurboSign PHP)
• `docs/SDKs/go.md` (TurboSign Go)
• `docs/SDKs/java.md` (TurboSign Java)
• `docs/SDKs/deliverable-*.md` (5 files)
• `docs/SDKs/partner-*.md` (4 files — Java pending)
• `docs/SDKs/webhooks-php.md` (and future `webhooks-javascript.md`, etc. as they ship)

Proposed callout

```md
:::tip Using Claude Code, Cursor, Copilot, or another AI coding tool?
Skip the manual setup. Run `/turbodocx-sdk` to have the TurboDocx Quickstart skill detect your project, install the SDK, generate config + routes + env vars, and wire everything into your app.

For TurboWebhooks specifically: `/turbodocx-sdk turbowebhooks`.
```

Acceptance criteria

• Every SDK reference page above has the callout near the top of the page (after the H1 / opening paragraph, before Installation).
• The callout mentions the specific subcommand relevant to that page (e.g. `/turbodocx-sdk turbosign` on TurboSign pages, `/turbodocx-sdk deliverable` on Deliverable pages, `/turbodocx-sdk turbowebhooks` on Webhooks pages).
• A single "Using an AI coding tool?" section is added near the top of `docs/SDKs/index.md` summarizing all the available subcommands and linking to the quickstart repo.

References

• Quickstart skill repo: https://github.com/TurboDocx/quickstart
• Current TurboWebhooks PHP skill coverage: TurboDocx/quickstart#3
• End-to-end example tracker in the quickstart repo: TurboDocx/quickstart#4

Start with docs/SDKs/index.md and compare the existing headings and admonition style across the JavaScript, Python, PHP, Go, Java, deliverable-, partner-, and webhooks-php.md pages. Add the relevant Quickstart callout near the top of each listed page, using the page’s subcommand. Done means every current SDK reference page has the appropriate callout and the index summarizes the available commands with the repository link.