docs: Add framework CLI command reference

[Zfinix]

Problem

The framework serverpod CLI had no command reference in the docs. The Tools section covered insights, lsp, run-scripts, and shell-completion, but there was no per-command reference for serverpod create, generate, create-migration, and the rest. The Serverpod Cloud CLI already has a full reference; the framework CLI did not.

Solution

Adds a CLI command reference under the Reference section at docs/06-concepts/23-cli/, mirroring the structure of the Serverpod Cloud CLI reference:

• Introduction, Global Options, Environment Variables, and a Commands section with one page per command.
• 12 commands documented: cloud, completion, create, create-migration, create-repair-migration, generate, language-server, mcp-server, quickstart, run, upgrade, and version.
• Each command page combines a hand-written intro (_<command>.md) with an auto-generated usage block (_generated/<command>.md) through a .mdx composer, the same pattern the Cloud reference uses.

The usage blocks are generated from serverpod 3.5.0-beta.10 with util/generate_cli_reference.sh, an interim in-repo generator. A CLI-driven sync bot in the monorepo (like the Cloud serverpod-cloud-docs-sync bot) is being discussed separately to keep these in sync automatically.

Closes #609.