fix(plugin): stop CI installing the jq the hooks no longer use (#4107)

Three loose ends from a49e7ed, all found by CI or by re-reading it.

TWO TESTS PINNED THE jq SYNTAX, not the word `jq`, so grepping the suite for
the tool name missed them: test_write_path_trigger asserted the literal filter
strings `(.note_ids // []) - (.sync_note_ids // [])` and `(.rule_ids // [])[]?`
appear in the hook. Re-spelled with the readers that replaced them. The claim
each makes is unchanged — that the reuse and sync channels keep their own
state file, their own query parameter and their own write-back.

CI STILL INSTALLED jq, TWICE. The "Install jq for hook execution tests" step
existed because those tests skipped rather than failed without it; the Plugin
hooks job installed it alongside shellcheck for the same reason. Removing a
dependency from the product and leaving CI to install it anyway means the
smoke tests never run under the condition they exist to assert. Both gone —
the hook tests now run on a bare image.

`awk 'END { print $0 }'` IS UNDEFINED IN POSIX. gawk retains the last record
in END and mawk does too, but it is not guaranteed, and reaching for a
non-portable idiom inside the change whose entire purpose is portability is
the same mistake one layer down. Now `{ last = $0 } END { if (NR) print last }`.
Verified it still selects the same start line on a real transcript.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

tests/test_write_path_trigger.py

@@ -1091,8 +1091,9 @@ def test_hook_keeps_sync_and_reuse_dedup_apart():
     assert ".sync.ids" in src                       # its own state file
     assert "exclude_sync_ids=" in src               # its own query channel
     # The reuse file must NOT swallow sync ids — the write-back subtracts them.
-    assert "(.note_ids // []) - (.sync_note_ids // [])" in src
-    assert "(.sync_note_ids // [])[]?" in src
+    # Spelled with the readers that replaced jq (#4107); the claim is unchanged.
+    assert "scribe_json_list_minus \"$body_flat\" '.note_ids' '.sync_note_ids'" in src
+    assert "scribe_json_list \"$body_flat\" '.sync_note_ids'" in src
 
 
 def _hook_runtime_env():
@@ -1668,7 +1669,7 @@ def test_hook_keeps_the_rule_channel_apart_from_the_other_three():
     src = HOOK.read_text()
     assert ".rules.ids" in src                      # its own state file
     assert "exclude_rule_ids=" in src               # its own query channel
-    assert "(.rule_ids // [])[]?" in src            # its own write-back
+    assert "scribe_json_list \"$body_flat\" '.rule_ids'" in src   # its own write-back
     # And it rides the same request as the rest, not a second round trip.
     assert "${rule_exclude_q}" in src