Improve missing vendor CLI errors and document prerequisites #1062

Description

Some ts commands invoke external vendor CLIs such as Fastly, Wrangler or Spin. When a required executable is absent, an ordinary process spawn error gives little guidance about which tool to install or which command needs it. The ts CLI delegates several build, deploy and config commands to edgezero_cli; identify the actual invocation points before adding checks.

Proposed fix

At each command that starts a vendor CLI, translate an executable-not-found failure into an error naming the missing program, the affected ts command and the installation or prerequisite documentation. Document the corresponding prerequisites in CLI help and the operator guide. Commands with no vendor CLI invocation should run without an unrelated preflight.

Done when

• For each affected adapter command, a missing vendor CLI produces an actionable error and a nonzero exit.
• Tests cover missing-tool behavior and confirm commands that do not invoke a vendor CLI need no such tool.
• CLI help and operator documentation list prerequisites at the relevant command/adapter level.
• Other spawn failures remain distinguishable from executable-not-found errors.

Affected area

CLI / adapter tooling / operator documentation.