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.

shopdb/__init__.py

@@ -130,7 +130,16 @@ from .plugins import plugin_manager
 # for an enrolled PC (401 SHARED_KEY_REFUSED), and maps a PermissionError from
 # apply_collector_payload to 403 ASSET_MISMATCH. All optional, so a plugin that
 # declares none of it is unaffected. Additive, minor bump.
-__contract_version__ = '0.33.0'
+# 0.34.0 adds BusinessUnit to the core model surface. It was the one thing an
+# asset carries that a plugin could not name: the endpoints fleet-alert scope
+# resolves a business unit per poll, and with no contract name for it the route
+# had dropped to db.text('SELECT businessunit FROM businessunits ...') against a
+# core table. That workaround respects the letter of ADR-002 and defeats its
+# point - a raw query is hidden coupling to the core schema that no contract
+# bump can catch, and it is the kind of thing that gets copied. Exposing the
+# model closes the gap instead of leaving the workaround as the worked example.
+# Additive name on the surface, minor bump.
+__contract_version__ = '0.34.0'
 
 # Product release version (see ADR-007). The product version and the
 # plugin-contract version above are distinct series with independent