Distinguish unsatisfied extension dependency constraints

[Copilot]

Extension dependency resolution treated an unsatisfied version constraint as a missing dependency, producing misleading diagnostics.

• Resolution

  • Retry by dependency ID within the parent’s source when a constrained lookup returns no matches.
  • Preserve existing successful and cross-source resolution behavior.

• Diagnostics

  • Add DependencyVersionNotFoundError to distinguish constraint failures:

    dependency azure.ai.inspector required by azure.ai.agents was found, but no version satisfies constraint ">=1.2.0"
    

  • Retain the existing not-found error when the dependency ID is absent.

• Coverage and documentation

  • Add regression coverage for both failure modes.
  • Document same-source dependency resolution and constraint mismatch guidance.

• Fixes [microsoft.azd.extensions] Extension dependency install failure poorly distinguishes error #8944

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[Copilot]

Pull request overview

Improves extension dependency diagnostics by distinguishing missing dependencies from unsatisfied version constraints.

Changes:

• Adds a typed constraint-mismatch error and same-source retry.
• Adds regression tests for both failure modes.
• Documents resolution behavior and troubleshooting.

Show a summary per file

File	Description
cli/azd/pkg/extensions/manager.go	Classifies dependency resolution failures.
cli/azd/pkg/extensions/manager_test.go	Tests failure classification.
cli/azd/docs/extensions/extension-resolution-and-versioning.md	Updates diagnostic guidance.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Balanced