fix(stop): a row-less stop uses the environment's server; only "no row" is row-less (Issue #71)

With no --herdr-session the server is chosen as create_session.sh chose
it (HERDR_SESSION_NAME, else the workspace's), not always derived from
the workspace. The row-less path runs only when the lookup says the row
is missing (exit 7); any other lookup failure stops with exit 1 as
before. Pins of the shifted stop_session.sh lines updated.

Refs #71

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/data/skill_code_blocks.json

@@ -433,7 +433,7 @@
    "class": "c",
    "kind": "diagram",
    "evidence": [
-    "multi-agent-mux-stop/scripts/stop_session.sh:228-242"
+    "multi-agent-mux-stop/scripts/stop_session.sh:240-254"
    ],
    "mismatch": null,
    "note": "state machine"
@@ -504,8 +504,8 @@
    "class": "a",
    "evidence": [
     "multi-agent-mux-stop/scripts/stop_session.sh:101",
-    "multi-agent-mux-stop/scripts/stop_session.sh:120-176",
-    "multi-agent-mux-stop/scripts/stop_session.sh:228-232"
+    "multi-agent-mux-stop/scripts/stop_session.sh:123-188",
+    "multi-agent-mux-stop/scripts/stop_session.sh:240-244"
    ],
    "mismatch": [
     "T1: the doc offered --force-no-yaml, which no script accepts"
@@ -601,7 +601,7 @@
     "other"
    ],
    "passthrough": {
-    "1": "multi-agent-mux-stop/scripts/stop_session.sh:367"
+    "1": "multi-agent-mux-stop/scripts/stop_session.sh:379"
    }
   },
   "multi-agent-mux-create/scripts/create_session.sh": {