toolkit merge: pre-shape CLI into packages/cli + apps/cli-docs

[BYK]

Sub-task of the toolkit monorepo merge (master issue linked below). Plan: https://gist.github.com/BYK/8c0ce6cec64608f41fe5654b7827228e

Pre-shape getsentry/cli into subtree layout (in-place PR) so it can be
imported into the renamed toolkit repo with zero root collisions.

• Move the CLI package root into packages/cli/ (its src/, test/, script/, patches/, plugins/, install, package.json).
• Move docs/ -> apps/cli-docs/.
• Add a local pnpm-workspace.yaml so the pre-shaped repo builds standalone.
• Keep CI green (generate pipelines, build, tests) in the new layout.

Rationale: MCP already occupies bin/, docs/, scripts/, plugins/ at root;
a single subtree prefix per tree avoids collisions. See §2.1.

[BYK]

Master tracking issue: #1248

[BYK]

PR opened: #1254