feat(app): allow pinning system-software versions on app create

[martin-helmich]

Summary

Closes #1951.

mw app create php|node|python previously offered no way to choose the runtime / system-software version — the newest available version was always assigned, so version-sensitive apps (e.g. Shopware 6.6 on PHP 8.5) would fail to start and required a second mw app dependency update call.

This adds a --set <dependency>=<version> flag to the custom-runtime create commands (php, php-worker, node, python) that pins the system-software version right after the installation is created, mirroring the existing mw app dependency update --set syntax.

mw app create php --document-root /public --set php=~8.3
mw app create node --set node=~18

Changes

• Extracted the dependency-resolution logic from app dependency update into a shared updateAppDependencies helper (src/lib/resources/app/dependencies.tsx), now used by both the create flow and the update command.
• Added the multi-valued set flag to the shared app flag set and wired it into the four custom-runtime create commands via AppInstaller.
• AppInstaller.exec applies the pinned versions (update policy patchLevel) after creating the installation and before waiting for it to normalize.
• Filtered non-scalar flags out of the userInputs payload in triggerAppInstallation so the array-valued set flag isn't serialized as a user input.
• Added usage examples to the php, node, and python create commands.

Note: the README/docs could not be regenerated in this environment (oclif readme fails with an unrelated LRUCache is not a constructor error); docs should be regenerated before merge.

🤖 Generated with Claude Code

[martin-helmich]

Converted back to draft status; there's an API change in the works that would allow us to set the system software versions with a single API call while installing the app.