Default ATVM automation commands to gold config files

Stop defaulting to cypress.atvm-config.ts in ATVM guidance.

Prefer gold-named config files unless explicitly told otherwise.

Update automation examples to use cypress.atvm-config-gold.ts.

Record the run learning explaining why the old default is unreliable.

atvm/AGENTS.md

@@ -150,6 +150,8 @@ Re-create blacklist:
 - Do not include Gold Disk IDs in `--build_name`.
 - `--build_name` must not contain spaces; use `-` between words.
 - Prefer distro-scoped filtering (for example `--containsVm redhat9`) when possible.
+- Do not reference `cypress.atvm-config.ts` by default.
+- Unless the operator explicitly asks for another config, use ATVM config files with `gold` in the filename (for example `cypress.atvm-config-gold.ts`).
 
 ## Update Policy (Both Tracks)
 After each run: