fix: omit empty project and language keys in azure.yaml

[huimiu]

Problem

azd ai agent init generates an azure.yaml where the code-less resource service (host: azure.ai.project) is written with project: "" and language: "":

services:
  hui-proj-ncus:
    project: ""
    host: azure.ai.project
    language: ""
    ...

The azure.yaml schema disables project for these code-less hosts ("project": false for azure.ai.project, azure.ai.connection, azure.ai.toolbox, azure.ai.skill, azure.ai.routine), so the generated file fails validation with "Property project is not allowed."

Root cause

ServiceConfig.RelativePath (yaml:"project") and ServiceConfig.Language (yaml:"language") had no omitempty, so project.Save always emitted them — even for code-less resource hosts that legitimately have no source path or language.

Fix

Add omitempty to RelativePath and Language. Traditional/container hosts always set these, so their output is unchanged; only empty values (code-less hosts) are now omitted.

Tests

Added TestCodelessServiceOmitsProjectAndLanguage verifying an azure.ai.project service serializes without project:/language: keys. Full pkg/project and internal/grpcserver suites pass.

[github-actions]

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[Copilot]

Pull request overview

This PR fixes azure.yaml generation/saving so code-less resource hosts (e.g., host: azure.ai.project) no longer serialize invalid empty project: "" and language: "" keys that violate the schema.

Changes:

• Add omitempty to ServiceConfig.RelativePath (project) and ServiceConfig.Language (language) YAML tags so empty values are not written.
• Add a regression test ensuring a code-less service host serializes without project: / language: keys.
• Add a changelog entry under Bugs Fixed documenting the schema-validation fix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
cli/azd/pkg/project/service_config.go	Updates YAML tags so empty project/language fields are omitted during save, avoiding invalid output for code-less hosts.
cli/azd/pkg/project/project_test.go	Adds a test that saves an azure.ai.project service and asserts project:/language: are not emitted.
cli/azd/CHANGELOG.md	Documents the bug fix in the Unreleased “Bugs Fixed” section.

[huimiu]

Superseded: moved this change into #8917 (branch hui/fix-foundry-project-name).