Answer a nonsense filter with a 400, and sweep every list route for the rest

Wave 3. Six findings, one cause: `int(request.args.get('typeid'))` with nothing
catching the ValueError. The caller sent a bad argument and got
500 INTERNAL_ERROR plus a traceback in the log, which says the server is broken
when the truth is that 'abc' is not a number.

shopdb/utils/queryargs.intarg reads it and raises QueryArgError, which an
app-level handler answers as a 400 naming the argument. App-level on purpose: a
route should not have to remember, and forgetting was the entire defect. The
policy differs from get_pagination_params, which falls back to a default for a
bad page number - a nonsense page is harmless and the caller still wants their
list, but silently ignoring a nonsense FILTER returns rows they believe they
excluded.

The gate matters more than the six fixes. tests/test_core/test_bad_query_args.py
sweeps all 131 registered no-parameter GET routes under /api/ with twelve
argument shapes and fails on any 5xx. It found sites the test run had not
reported - statusid and locationid on /api/assets, the second asset-list route,
limit on the employee lookup and the printer supply history - because the
pattern is how a list filter gets written rather than a property of any one
route. Verified non-vacuous by planting the old `int(...)` back into
/api/machines: four tests fail.

Four usb routes are skipped by exact path, with the reason: they reach the
EXTERNAL cmmc_usb database, so their 500 in a test environment is a missing
database rather than an argument fault. That is the complete set - every usb
GET route calling cmmc_usb_connection - not a convenient subset.

One correction worth recording: the first pass rewrote every
`if x := request.args.get(...)` in the touched files, including text arguments,
so a search for 'ZZNOTHINGMATCHES' briefly became a 400. Caught by
test_list_search_identifiers. Only id-shaped arguments are integers.

Scope: product

plugins/computers/api/routes.py

@@ -7,7 +7,7 @@ from shopdb.api import db, Asset, AssetType, OperatingSystem, Application, Audit
 
 from ..models import Computer, ComputerType, ComputerInstalledApp, AccessProtocol, ComputerAccess
 
-from shopdb.api import require_permission, require_role, apply_import_timestamps
+from shopdb.api import require_permission, require_role, apply_import_timestamps, intarg
 
 computers_bp = Blueprint('computers', __name__)
 
@@ -380,20 +380,20 @@ def list_computers():
         )
 
     # Computer type filter
-    if type_id := request.args.get('typeid', request.args.get('type_id')):
-        query = query.filter(Computer.computertypeid == int(type_id))
+    if (type_id := intarg('typeid', intarg('type_id'))) is not None:
+        query = query.filter(Computer.computertypeid == type_id)
 
     # OS filter
-    if os_id := request.args.get('osid', request.args.get('os_id')):
-        query = query.filter(Computer.osid == int(os_id))
+    if (os_id := intarg('osid', intarg('os_id'))) is not None:
+        query = query.filter(Computer.osid == os_id)
 
     # Location filter
-    if location_id := request.args.get('locationid', request.args.get('location_id')):
-        query = query.filter(Asset.locationid == int(location_id))
+    if (location_id := intarg('locationid', intarg('location_id'))) is not None:
+        query = query.filter(Asset.locationid == location_id)
 
     # Business unit filter
-    if bu_id := request.args.get('businessunitid', request.args.get('businessunit_id')):
-        query = query.filter(Asset.businessunitid == int(bu_id))
+    if (bu_id := intarg('businessunitid', intarg('businessunit_id'))) is not None:
+        query = query.filter(Asset.businessunitid == bu_id)
 
     # Shopfloor filter (by the Shopfloor computer type)
     if shopfloor := request.args.get('shopfloor'):