fix(jira): report which admin config field is actually missing

POST /system/jira-test bundled 4 independent checks (enabled, url,
admin_email, admin_api_token) behind has_admin_jira_configured() but
always blamed "Admin Email and Admin API Token" regardless of which one
failed. Found via live QA: URL/email/token were all correctly saved, but
the "Enable Jira Integration" toggle was never switched on — the error
message pointed at the wrong fields, making it look like the already-set
credentials were missing.

backend/app/routers/system.py

@@ -354,7 +354,7 @@ def test_jira_connection(
     """
     from app.services.jira_service import (
         get_admin_jira_client, get_jira_url, has_admin_jira_configured,
-        get_admin_jira_email,
+        get_admin_jira_email, get_admin_jira_api_token, is_jira_enabled,
     )
 
     jira_url = get_jira_url(db)
@@ -362,12 +362,21 @@ def test_jira_connection(
         return {"status": "error", "message": "Jira URL is not configured.", "jira_url": ""}
 
     if not has_admin_jira_configured(db):
+        # has_admin_jira_configured() bundles 4 independent checks into one
+        # bool — report exactly which one(s) are actually missing instead of
+        # always blaming "Admin Email and Admin API Token" regardless of
+        # which check failed (e.g. URL/email/token can all be set while the
+        # "Enable Jira Integration" toggle itself is still off).
+        missing = []
+        if not is_jira_enabled(db):
+            missing.append("Jira integration is not enabled (toggle 'Enable Jira Integration' above)")
+        if not get_admin_jira_email(db):
+            missing.append("Admin Email is not set")
+        if not get_admin_jira_api_token(db):
+            missing.append("Admin API Token is not set")
         return {
             "status": "error",
-            "message": (
-                "Admin Jira credentials not configured. "
-                "Set the Admin Email and Admin API Token in the fields above."
-            ),
+            "message": "Cannot connect: " + "; ".join(missing) + ".",
             "jira_url": jira_url,
         }