Guard edge-app create against EDGE_APP_ID, warn on stale id after delete

[nicomiguelino]

Summary

• edge-app create and edge-app create --in-place now refuse to run while EDGE_APP_ID is set. Both commands always create a brand new Edge App, so proceeding with the env var already set would leave it pointing at an app the user didn't mean to create. The error message names the current value and suggests unsetting EDGE_APP_ID or using edge-app deploy instead.
• edge-app delete still clears id from screenly.yml via clear_app_id, unchanged. It now also prints a warning if EDGE_APP_ID is still set afterward, since the CLI has no way to clear an environment variable on the user's behalf and would otherwise silently keep resolving to the deleted app on the next command.
• Extracted the env var read into a shared edge_app_id_from_env() helper (trims and treats whitespace only as unset, matching the manifest's existing validation), reused by get_app_id, create, create_in_place, and the delete flow in cli.rs.
• Docs updated in docs/EdgeApps.md under the manifest id reference to describe both behaviors.

[Copilot]

Pull request overview

This PR strengthens Edge App CLI safety around EDGE_APP_ID by preventing accidental creation while an app id is already configured, and by warning after deletion when an env-configured id may now be stale.

Changes:

• Add a shared edge_app_id_from_env() helper (trim + whitespace-only treated as unset) and reuse it in get_app_id, create, create --in-place, and the delete flow.
• Make edge-app create / edge-app create --in-place error out when EDGE_APP_ID is set, and add unit tests for the behavior.
• After successful edge-app delete, warn if EDGE_APP_ID remains set; update docs to describe these behaviors.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/commands/edge_app/app.rs	Adds env-var helper and guards create/create_in_place; updates get_app_id; adds tests.
src/cli.rs	Emits a post-delete warning if EDGE_APP_ID is still set.
docs/EdgeApps.md	Documents the new guard/warning behavior around EDGE_APP_ID.

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[Copilot]

Pull request overview

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

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

Suppressed comments (1)

src/commands/edge_app/app.rs:207

• This error message also refers to 'edge-app deploy', but the CLI is invoked as screenly edge-app …. Using the full command name avoids confusion and matches other user-facing guidance strings.

        if let Some(id) = edge_app_id_from_env() {
            return Err(CommandError::InitializationError(format!(
                "An Edge App id is already configured via the {EDGE_APP_ID_ENV} environment variable ({id}). The operation can only proceed when no Edge App id is already configured; unset {EDGE_APP_ID_ENV} first if you want to create a new Edge App, or use 'edge-app deploy' if you meant to deploy to the existing app."
            )));

[Copilot]

Pull request overview

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

[nicomiguelino]

Upcoming commits to #315 will supersede this pull request.