docs: Realign How it works around the hot-reload dev loop

[developerjamiu]

Summary

Realigns the How it works page (#566) to lead with the developer experience, the serverpod start hot-reload dev loop, rather than internal request mechanics.

• New structure: what you build → the dev loop → an AI-assisted workflow → choices at serverpod create → why it works → next steps.
• Removes the request-lifecycle section and the mermaid sequence diagram (per Realign How it works with new the hot-reload workflow #566).
• Documents the dev loop (one-command hot reload, embedded Postgres, no Docker by default), the optional AI-assisted workflow (editor agent skills + MCP server), and the serverpod create choices.
• Surfaces the batteries-included differentiator: database, authentication, file uploads, caching, and real-time are built in.
• Adds launch-pad links to the endpoints, models, sessions, streams, modules, and deployment docs.
• Keeps the page name and slug (/how-it-works); does not introduce the "Jetstream" brand (per Realign How it works with new the hot-reload workflow #566).

Verification

• Technical claims checked against the framework source: serverpod start behavior, embedded Postgres as the default (confirmed against a 3.5 project), the serverpod create choices, client.example.hello, and .spy.yaml.
• markdownlint passes; no em dashes; cross-doc links use slug form.
• I did not run npm run build locally (per AGENTS.md). Please confirm the cross-doc links resolve in the build, this page uses a custom /how-it-works slug, so the slug-form links are worth a build check.

Closes #566

[vlidholt]

I think this page should function as a "quickstart" to understand how to work with Serverpod. Not how Serverpod works under the hood. What will the user need to know to get started as quickly as possible, without going through the getting-started guide? This is basically the page for more experienced Flutter developers who want to get started quickly.

Having a brief introduction at the top, as we do now, is great. But we must also dive a bit deeper into how you define a model and what you can pass to your methods. The old overview covers this pretty neatly. If we can take the good stuff from there and add it into this page, that would be ideal.

https://docs.serverpod.dev/overview

[vlidholt]

See comment above.

[vlidholt]

Proposed some changes.

[vlidholt]

LGTM! 🥳