Validate missing solution

[TomProkop]

Title

pp-entity creation should fail input validation when solution metadata root is missing

Summary

Creating a pp-entity in an empty output folder currently reaches post-actions and fails late in AddEntityToSolutionXml.ps1 because Other/Solution.xml is missing. This should be rejected during input validation before scaffolding starts.

Steps to Reproduce

1. Create an empty folder: temp/txc-entity-demo
2. Run:

txc ws comp create pp-entity \
  -o temp/txc-entity-demo \
  --param Behavior=New \
  --param LogicalName=temporaryentity \
  --param LogicalNamePlural=temporaryentities \
  --param DisplayName='Temporary Entity' \
  --param DisplayNamePlural='Temporary Entities' \
  --param PublisherPrefix=tmp

Actual Result

• Output says template creation started/succeeded.
• Post-action AddEntityToSolutionXml.ps1 fails because ./Other/Solution.xml does not exist.
• Operation rolls back after doing work.

Representative error:

Cannot find path '.../temp/txc-entity-demo/Other/Solution.xml' because it does not exist.
Post-action(s) failed, all changes rolled back: Adding entity to solution.xml

Expected Result

The CLI should fail during input validation with a clear message before scaffolding:

• Required structure is missing (for example Other/Solution.xml).
• User must create/initialize a proper solution first, then run pp-entity creation.

Proposed Change

Add pre-flight validation for pp-entity creation:

1. Validate output target contains a valid solution metadata root.
2. If validation fails, stop immediately with non-zero exit code.
3. Return a direct, actionable error, for example:
   • "Invalid target folder for pp-entity: missing Other/Solution.xml. Initialize or create a solution structure first."