fix(gtea): derive STACK_NAME from domain (dots→underscores) in UPGRADE_SECRET_PREP

abra does NOT write STACK_NAME to the app's .env file — it derives it at runtime
by replacing dots with underscores (e.g. gite-e1cb78.ci.commoninternet.net →
gite-e1cb78_ci_commoninternet_net). Build #691 failed with 'STACK_NAME not found'
because the env file read was looking for a key that doesn't exist.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/gitea/recipe_meta.py

@@ -71,18 +71,9 @@ def UPGRADE_SECRET_PREP(ctx):
     import base64
     import subprocess
 
-    env_path = _os.path.expanduser(f"~/.abra/servers/default/{ctx.domain}.env")
-    stack_name = None
-    try:
-        with open(env_path) as fh:
-            for line in fh:
-                if line.startswith("STACK_NAME="):
-                    stack_name = line.split("=", 1)[1].strip().strip('"').strip("'")
-    except OSError:
-        pass
-    if not stack_name:
-        raise RuntimeError(f"UPGRADE_SECRET_PREP: STACK_NAME not found in {env_path}")
-
+    # abra derives STACK_NAME from the domain by replacing dots with underscores
+    # (e.g. gite-e1cb78.ci.commoninternet.net → gite-e1cb78_ci_commoninternet_net).
+    stack_name = ctx.domain.replace(".", "_")
     docker_secret = f"{stack_name}_lfs_jwt_secret_v1"
     value = base64.urlsafe_b64encode(_os.urandom(32)).rstrip(b"=").decode()