Rebrand: update ".NET Aspire" references to "Aspire"

[IEvangelist]

Background

The product formerly known as .NET Aspire was rebranded to simply Aspire in late 2024. Several current, user-facing references in azd still use the old ".NET Aspire" name and should be updated to align with the current branding.

Scope

Update active references in documentation, user-facing CLI strings, and code comments:

• cli/azd/internal/cmd/add/add.go — the azd add incompatibility suggestion string ("does not support .NET Aspire projects.")
• cli/azd/docs/environment-variables.md — descriptions for AZURE_APP_SERVICE_DASHBOARD_URI, AZD_DEBUG_DOTNET_APPHOST_USE_FIXED_MANIFEST, and AZD_DEBUG_DOTNET_APPHOST_IGNORE_UNSUPPORTED_RESOURCES
• cli/azd/extensions/microsoft.azd.concurx/README.md — four mentions in the extension docs
• docs/reference/telemetry-data.md — the containerapp-dotnet host description
• eng/pipelines/templates/jobs/build-cli.yml — pipeline comment

Out of scope

• cli/azd/CHANGELOG.md — historical release-note entries are deliberately left unchanged. They reflect the product name at the time of each release; rewriting them would misrepresent that history.
• Identifiers/values such as the containerapp-dotnet telemetry value and *_DOTNET_APPHOST_* env-var names are not display names and remain unchanged to avoid breaking compatibility.

Acceptance criteria

• No current/active ".NET Aspire" references remain outside of CHANGELOG.md.
• Spelling, formatting, and build/lint checks pass.