Make the server authoritative for what endpoints watch and launch

Fleet health showed dncMain.exe red on endpoints that never ran eDNC. Three
layers each re-added the monitor, so fixing any one of them in isolation left
the others to put it back.

The installer baked a watch list into appsettings.json on every package, and
appsettings.json is never rewritten on the box, so an entry outlived whatever
policy justified it. The server auto-attached shipped monitors by PC type name.
The agent then UNIONED the server's resolved list with its local one, so an
entry could never be removed from the server side at all.

Now: the installer seeds nothing, auto-attach by PC type is gone, and
MonitorConfig.Merge replaces the local list with the server's. Null and empty
stay distinct - null means the fetch failed so keep what we have, empty means
watch nothing. Collapsing those blanks monitoring fleet-wide on one failed HTTP
call, or makes detaching the last monitor silently do nothing forever.

Ingest filters reported services against the resolved monitors as well. The
agent config sits on the endpoint, so it is not a trustworthy account of what
that endpoint should be reporting.

Launch paths move the same way, which exposed an older bug. MTConnect installs
to ProgramData and starts through run.bat, but LaunchPathPolicy approved only
the Program Files roots, so the launchpath on its shipped monitor row - seeded
in 0006, present from the start - was rejected every time as outside every
approved root. That was invisible because a local launchpaths entry wins in
ResolveLaunchPath and never reaches validation; remote start worked only
through the bypass. The same precedence meant editing an eDNC, UDC or MTConnect
path in the WebUI could never reach an existing endpoint.

So ProgramData is approved and the local launch map ships empty. ProgramData is
world-writable and the agent launches as SYSTEM, which is why it was excluded
originally; it is deliberately too broad for now and carries a REVISIT comment.
The remaining gates still hold - admin-configured monitor row, exists,
launchable extension, re-checked after symlink resolution. Narrowing it to
ProgramData\udc needs the fleet's non-Program-Files install locations
confirmed first.

Also seeds the Office ProPlus LTSC monitor templates, x64 and x86 as separate
rows since they differ only by path, and adds an agent test project. It links
the platform-pure sources rather than referencing the net8.0-windows assembly
so the semantics run on the Linux CI runners. Writing those tests caught a
merge bug where only the dedupe key was trimmed and the stored name was not.

Note for the wj merge: plugins/usb/frontend/views/usbSettings.spec.js fails on
this branch and is untouched here. Commit da91a29 added four kiosk settings the
save assertion does not expect. The spec looks like the stale side, but that is
the usb author's call - flagging rather than guessing.

.github/workflows/ci.yml

@@ -87,6 +87,24 @@ jobs:
       - run: npx vitest run
       - run: npm run build
 
+  agent:
+    # Semantic checks on the endpoint agent's pure logic. Until this existed the
+    # agent had no tests at all, so a change to what an endpoint watches - or to
+    # the guard that decides which paths it will execute - was reviewed by
+    # reading alone.
+    #
+    # The project targets net8.0 and links the platform-pure sources rather than
+    # referencing ShopDbEndpointAgent.Core, which is net8.0-windows and cannot
+    # run here. See the csproj header for why, and for what that trades away.
+    # Runs in well under a second; it does not meaningfully add to gate time.
+    runs-on: arc-runner-set
+    steps:
+      - uses: actions/checkout@v5
+      - uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: '8.0.x'
+      - run: dotnet test agent/ShopDbEndpointAgent.Core.Tests/ShopDbEndpointAgent.Core.Tests.csproj --nologo
+
   lean-build:
     # ADR-013 Phase 5: prove a per-site build carries only its chosen plugins.
     # The profile is the WJ plugin set, so this job proves the build this branch