Backend: Implement template apply engine (remove + copy)

[acn-sbuad]

Description

Implement logic to apply a template to an app repo creation process.

Steps

0. Copy default repo
1. Remove:
   • Expand globs in remove
   • Delete files/folders
2. Copy:
   • Copy <template>/<contentPath> → app root
   • Overwrite existing files
3. update appmetadata

steps 1 and 2 handled by template apply engine

Safety

• Never delete outside app root
• Reject path traversal
• No-op if remove matches nothing

Acceptance criteria

• Directories and files are removed correctly.

• Copy overwrites existing files.

• Safety checks prevent deleting outside root.

• Logs removed + copied files.

• Unit tests cover all behaviors.

• Apply template during app initialization

• If no templateId → use default behavior

• API accepts optional templateId

• Unknown templateId → 400 error

• Template applied in correct order

• Integration test covers create-app with template