Simplify azd ai agent/finetuning init to use --minimal flag

[Copilot]

When no azd project exists, azd ai agent init and azd ai finetuning init call azd init interactively, presenting users with three confusing options ("Scan current directory", "Select a template", "Use agent mode"), which users may not know what to pick.

This PR simplifies this flow by defaulting to azd init --minimal, effectively reducing the number of init/env-related prompts from 4 to 2:

Changes

• Both extensions: Changed ensureProject to call azd init --minimal instead of azd init
• Removed -e environment flag from init call (not supported by --minimal; environment creation already handled separately in ensureEnvironment)

// Before
initArgs := []string{"init"}
if flags.env != "" {
    initArgs = append(initArgs, "-e", flags.env)
}

// After
initArgs := []string{"init", "--minimal"}

• azure.ai.finetune - suppress Warning: failed to get existing environment log message

Environment handling continues to work via the existing ensureEnvironment function which runs azd env new after project initialization.

Original prompt

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This section details on the original issue you should resolve

<issue_title>AI extensions - consider simplifying azd ai agent/finetuning init to call azd init --minimal</issue_title>
<issue_description>Currently, if there's no azd project detected, azd ai agent/finetuning init calls azd init interactively, which presents 3 options:

We've gotten feedback it's not clear what users should pick here</issue_description>

<agent_instructions>When running 'azd init --minimal', the -e / --environment flag won't do anything, so we'll need to handle env creation separately.

Make changes to both azure.ai.finetune and azure.ai.agents extensions</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes AI extensions - consider simplifying azd ai agent/finetuning init to call azd init --minimal #6669

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[Copilot]

Pull request overview

This PR simplifies the initialization flow for AI extensions (azd ai agent init and azd ai finetuning init) by using the --minimal flag when calling azd init, avoiding confusing interactive prompts that ask users to choose between "Scan current directory", "Select a template", or "Use agent mode".

Changes:

• Modified both extensions to call azd init --minimal instead of azd init
• Removed the -e environment flag from init calls (not supported by --minimal; environment creation is handled separately via ensureEnvironment)
• Refactored getExistingEnvironment in finetune extension to suppress warning messages by silently handling lookup errors

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
cli/azd/extensions/azure.ai.finetune/internal/cmd/init.go	Updated ensureProject to use --minimal flag; refactored getExistingEnvironment to return only environment (no error) and silently ignore lookup failures; removed warning log in ensureEnvironment
cli/azd/extensions/azure.ai.finetune/go.mod	Moved stretchr/testify from indirect to direct dependency (used in tests)
cli/azd/extensions/azure.ai.agents/internal/cmd/init.go	Updated ensureProject to use --minimal flag and removed -e environment flag
.gitignore	Added binary output files for azure.ai.finetune extension

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