[management] Rework Agent Network endpoint identity and settings bootstrap (#7085)

Store the per-account gateway endpoint as {domain, proxy_address} with a
global unique index on the full hostname; dedicated = (domain ==
proxy_address). Bootstrap becomes an explicit POST carrying exactly one
of proxy_address (server allocates an adjective-noun label beneath it)
or endpoint (claimed verbatim, address-first); provider create loses its
bootstrap side effect. PUT is a full replace with every field required —
the immutable identity fields must be echoed unchanged and a mismatch is
rejected with 422. A guarded DELETE releases the endpoint: refused with
412 while providers exist or a proxy is actively serving the endpoint
hostname (matched case-insensitively); re-creating bootstraps fresh. A
self-addressed pin excludes its address from the account's cluster allow
list, and the live mapping update path now addresses the serving proxy
from the synthesized service. Existing rows are migrated on all three
store engines.

e2e/agentnetwork/chat_test.go

@@ -438,14 +438,10 @@ func TestProvidersMatrix(t *testing.T) {
 	// Create every provider, all enabled, each with a unique model string so the
 	// proxy's connect-time snapshot carries them all and model→provider routing
 	// is unambiguous (provider toggles after connect don't reconcile to the
-	// proxy, so we enable everything up front). The first create bootstraps the
-	// cluster.
+	// proxy, so we enable everything up front).
 	ids := make([]string, 0, len(matrix))
-	for i, pc := range matrix {
+	for _, pc := range matrix {
 		req := providerRequest(pc)
-		if i == 0 {
-			req.BootstrapCluster = ptr(harness.AgentNetworkCluster)
-		}
 		prov, perr := srv.CreateProvider(ctx, req)
 		require.NoError(t, perr, "create provider %s", pc.name)
 		ids = append(ids, prov.Id)