Migrate 1P extensions to azdext.NewExtensionRootCommand and remove reserved-flag conflicts

[Copilot]

Audits the remaining first-party extensions in cli/azd/extensions/ and migrates them to azdext.NewExtensionRootCommand, removing flags that collide with azd's reserved global flag set (--debug, --no-prompt, --cwd, -e/--environment, -o/--output, etc.). Mirrors the work already done for azure.ai.agents (#7947); microsoft.azd.extensions is intentionally out of scope (tracked in #7951).

Per-extension changes

• azure.ai.finetune — SDK root; init --environment/-n removed (reads extCtx.Environment); jobs show and jobs list swap their local -o/--output for azdext.RegisterFlagOptions (default table, allowed table,json[,yaml]).
• azure.ai.models — SDK root; init --environment/-n removed; custom show / custom list use RegisterFlagOptions for --output; custom delete reads --no-prompt from extCtx.
• azure.appservice — SDK root; swap reads --no-prompt from extCtx instead of the dropped rootFlagsDefinition.
• azure.coding-agent — SDK root; also drops the conflicting config --debug (the issue lists only the root flag, but the same --debug is re-registered on the subcommand and would still fail ValidateNoReservedFlagConflicts). Reads from extCtx.Debug.
• microsoft.azd.concurx — SDK root; duplicate up --debug removed (reads extCtx.Debug).
• microsoft.azd.demo — adopts NewExtensionRootCommand for consistency (no flag conflicts).

SDK version

azure.ai.finetune and azure.ai.models go.mod bumped to a cli/azd revision that includes RegisterFlagOptions (#7826). The other four extensions only depend on NewExtensionRootCommand (already in cli/azd v1.23.13) so their go.mod is unchanged. microsoft.azd.demo builds against the in-tree cli/azd module.

Migration shape

// Before
rootCmd := &cobra.Command{Use: "appservice <command> [options]", ...}
rootCmd.PersistentFlags().BoolVar(&rootFlags.Debug, "debug", false, "Enable debug mode")
rootCmd.PersistentFlags().BoolVar(&rootFlags.NoPrompt, "no-prompt", false, "...")
rootCmd.AddCommand(newSwapCommand(rootFlags))

// After
rootCmd, extCtx := azdext.NewExtensionRootCommand(azdext.ExtensionCommandOptions{
    Name:  "appservice",
    Use:   "appservice <command> [options]",
    Short: "Extension for managing Azure App Service resources.",
})
rootCmd.SilenceUsage = true
rootCmd.SilenceErrors = true
rootCmd.CompletionOptions.DisableDefaultCmd = true
rootCmd.AddCommand(newSwapCommand(extCtx))

// Per-subcommand --output via RegisterFlagOptions instead of a local -o flag
azdext.RegisterFlagOptions(cmd, azdext.FlagOptions{
    Name:          "output",
    AllowedValues: []string{"table", "json", "yaml"},
    Default:       "table",
})

[jongio]

The migration to NewExtensionRootCommand is a solid direction - centralizes flag management in the SDK and removes duplicated registration across extensions. CI is green.

Two things to address:

1. Breaking shorthand: -n removed for --environment

Both azure.ai.finetune and azure.ai.models init commands previously used -n as shorthand for --environment. The SDK uses -e. Users who relied on init -n myenv will get an error. Worth a CHANGELOG entry noting this change.

2. Pseudo-version dependency

Both finetune and models pin to a pseudo-version (v1.24.3-0.20260428202310-4d8945f915d8). Per AGENTS.md, extensions should use semver tags. Is there a planned SDK release before this merges, or is this intentionally temporary?

The updated SDK dependency also pulls in ~40 new indirect deps (Azure RM packages for cosmos, container registry, keyvault, machine learning, etc., plus copilot-sdk and azure-devops-go-api). None are used directly by these extensions. The comment in extension_command.go already notes the CLI helpers are candidates for extraction into an azdext/cobra sub-package - that'd help here.

[jongio]

This pseudo-version replaces the semver v1.23.13 tag. Per AGENTS.md convention, extensions should pin to semver tags (cli/azd/vX.Y.Z). If the SDK features this PR needs (RegisterFlagOptions, NewExtensionRootCommand) aren't in a released tag yet, consider coordinating the SDK release first, or add a TODO comment here noting it should be updated to the next stable tag.

[jongio]

This reads environment from extCtx.Environment (populated by the SDK's -e/--environment flag). Previously this command had -n as the shorthand for --environment. Users who relied on init -n myenv will break silently - they'll get an unknown shorthand flag error.

Aligning to -e is the right call long-term (matches azd convention), but this should be documented as a breaking change in the release notes.

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