Act on the wj architectural review: races, limits, pool and contract gaps

Findings F2, F4, F5, F6, F7, F8, F9, F10, F11 and F13 from
wj-architectural-review.md. F1/F1a (the non-sargable LOWER pattern) and F3
(the warranty sync holding a pooled connection) are being handled separately
and are untouched here.

- A collector check-in that raced another for the same PC lost everything:
  the unique index on the application fingerprint raised, nothing caught it,
  and the whole check-in rolled back, discarding state, events and hardware,
  answering the agent with form copy meant for a person. The insert now runs
  in a savepoint, reconciles what the other transaction already wrote, one row
  per savepoint so a second collision skips a row rather than the batch, and
  the check-in commits with a warning. This is the shape the delete side of
  the same function already had.
- Enrollment is deliberately unauthenticated, so it now carries a per-address
  rate limit and a cap on pending requests, and the cap is a setting an admin
  can see and change. A flood can no longer bury the approval queue or grow
  the table without bound.
- The fleet alert poll no longer formats debug strings on every request.
- BusinessUnit is on the contract surface (0.34.0), so the endpoints plugin
  stops reaching into a core table with raw SQL.
- A test walks every asset type descriptor and proves the endpoint it names
  really refuses a caller without the declared permission.
- The plugin settings routes now need a permission; they were telling anyone
  which modules a site runs and where its components live.
- The connection pool is sized explicitly with a short timeout, and the
  arithmetic against the server's connection ceiling is written next to the
  worker count instead of being left to defaults nobody chose.
- Fleet alerts carry both the correct lowercase keys and the old camelCase
  pair. Trays older than 1.7.0 match keys case-sensitively and would have gone
  quiet on every PC not yet upgraded; the old pair goes when they are.
- The dev server proxy points at localhost again, with environment variables
  for the remote-box workflow, and one developer's address is out of the
  server certificate page.

plugins/endpoints/frontend/views/enrollmentSettings.spec.js

@@ -54,7 +54,8 @@ function enrollmentPayload() {
   return {
     data: {
       data: {
-        settings: { sharedkeyallowed: true, autoenroll: true },
+        settings: { sharedkeyallowed: true, autoenroll: true,
+                    maxpendingenrollments: 500 },
         counts: { enrolled: 40, notenrolled: 58, pendingcomputers: 1, pending: 2 },
         computers: [
           { assetid: 21, hostname: 'PC-ENROLLED', serialnumber: 'S1', state: 'enrolled',
@@ -325,4 +326,20 @@ describe('EnrollmentSettings', () => {
     expect(api.put).not.toHaveBeenCalled()
     expect(toggle.element.checked).toBe(true)
   })
+
+  it('saves a new pending request limit', async () => {
+    const wrapper = await render()
+    await openCredentials(wrapper)
+    const field = wrapper.find('.input-maxpending')
+    expect(field.element.value).toBe('500')
+    await field.setValue(25)
+    await field.trigger('change')
+    await flushPromises()
+    expect(api.put).toHaveBeenCalledWith('/endpoints/enrollment/settings',
+      { maxpendingenrollments: 25 })
+  })
+
+  // The negative case is proved server side (tests/test_plugins/
+  // test_endpoints_enroll_limits.py: PUT with -1 is a 400). Asserting it here
+  // would only be asserting what vue-test-utils does to a number input.
 })