Report each Windows event once, and persist the inventory already sent

Curated events were re-read from the newest 25 entries per channel on every
collect, and the server appended whatever arrived. One real event was
therefore stored again on every cadence tick for as long as it stayed in
that window, so event counts measured how long a box had been up rather
than what had happened to it.

The agent now keeps a per-channel watermark of the last Windows event
record id it reported, persisted under ProgramData so a service restart
does not replay history, and sends eventrecordid with each event. The
server dedupes on (assetid, eventchannel, eventrecordid) behind a unique
index, so a replay from an older agent cannot double-store either.

Six inventory keys the agent had been sending all along - bios, disks,
domain, memory, osinfo, processor - were parsed, logged as unpersisted,
and dropped. They now have columns and are written on check-in, along
with user context, pending reboot, and the cpupercent/memorypercent/
idleseconds fields that were declared in the contract but always null.

Session-scoped data cannot be read from the agent's LocalSystem session 0
at all: mapped drives and user-owned listeners do not exist there. A probe
runs in the interactive user's session and hands results back through a
spool file. It is not yet producing output on a live endpoint; the column
and panel are in place and read empty until that is fixed.

Also bounds the user-context script wait. It was WaitForSingleObject with
INFINITE, so a hung script pinned the command worker permanently.

plugins/endpoints/commands.py

@@ -77,6 +77,12 @@ COMMAND_ALLOWLIST = {
         'label': 'Collect now',
         'description': 'Force the endpoint agent to report fresh telemetry off-cadence.',
     },
+    'network_connections': {
+        'label': 'Show network connections',
+        'description': 'Return the full TCP connection table with owning processes. '
+                       'Read-only diagnostic; the standard report carries only '
+                       'listening ports because established connections churn.',
+    },
     'run_script': {
         'label': 'Run script',
         'description': 'Run a ShopDB-hosted script on the endpoint. The agent '