Clear the Dependabot findings

Dependabot alerts were switched on for this repo today and reported 12 open
findings. Ten are fixed here; the other two are addressed below.

gRPC 1.83.0 -> 1.83.1, in all nine modules that require it. This is
GHSA-vp52-pcj8-j9qc / CVE-2026-84304, heap memory exhaustion via HTTP/2 DATA
frame fragmentation, affecting <= 1.83.0. It matters more than the version
delta suggests: ingest/ is a gRPC listener deliberately exposed to the internet
on :4317, so a remote OOM is reachable. mTLS narrows that to holders of a
client certificate, which is why this was not an emergency, but the fix is one
patch release away and there is no reason to carry it.

golang.org/x/oauth2 0.21.0 -> 0.27.0 in deploy/operator, an indirect
dependency (GHSA-6v2p-p543-phr9). enterprise/ was already past it at 0.36.0.

npm cookie 0.6.0 -> 0.7.2, via an overrides entry rather than a dependency
bump. @sveltejs/kit requires ^0.6.0 and still does at 2.70.3, the latest
release, so there is no version of kit that resolves this on its own -- an
override is the only route that does not involve waiting on upstream.

Three incidental changes came out of `go mod tidy` and are not mine:
genproto/googleapis/rpc moved forward as a transitive of the new grpc; pgx/v5
was reclassified from indirect to direct in enterprise/, which is simply
correct, since audit.go and cmd/enterprise-auth import it; and the proto
replace directive shuffled between require blocks at the same version.

The twelfth finding, lru (GHSA-rhfx-m35p-ff5j), is not fixed and is not
fixable here -- see the note in the pull request. It is CVSS 0, a Stacked
Borrows soundness issue in IterMut, and reaching a patched version means
tantivy 0.22 -> 0.26, which is a search engine migration rather than a
dependency bump.

Verified: all ten Go modules build, 40 test packages pass, the web app builds
and svelte-check reports 0 errors across 288 files.

hack/demo-hosts-fixture/go.mod

@@ -6,7 +6,7 @@ replace github.com/cairnobs/cairnobs/proto => ../../proto
 
 require (
 	github.com/cairnobs/cairnobs/proto v0.0.0-00010101000000-000000000000
-	google.golang.org/grpc v1.83.0
+	google.golang.org/grpc v1.83.1
 )
 
 require (