[management] Resolve agent network permissions per submodule (#7030)

## Describe your changes

Agent Network gates providers, policies, guardrails, budgets, usage,
access logs, and settings behind the single `agent_network` permission
module, so access is all-or-nothing: a future delegated role cannot be
scoped to a subset of the area (for example usage-only visibility).

This introduces dotted submodules (`agent_network.providers`,
`.policies`, `.guardrails`, `.budgets`, `.usage`, `.logs`, `.settings`)
and resolves grants with a cascade: exact module first, then its parent,
then the role's `AutoAllowNew` default. The agent network manager now
validates each operation against its matching submodule. `usage`
(aggregated counters, overview) is deliberately separate from `logs`
(request-level entries, which can contain captured prompts).

No role definitions change. No built-in role carries an explicit
`agent_network` entry, so every role resolves the submodules exactly as
it resolved the parent module before — pinned by a test that compares
each built-in role's answer on every submodule against its answer on
`agent_network`. Role additions that use these submodules come
separately.

management/server/permissions/modules/module.go

@@ -1,5 +1,7 @@
 package modules
 
+import "strings"
+
 type Module string
 
 const (
@@ -20,6 +22,17 @@ const (
 	IdentityProviders Module = "identity_providers"
 	Services          Module = "services"
 	AgentNetwork      Module = "agent_network"
+
+	// Agent Network submodules. A role may grant one of these directly
+	// or grant the AgentNetwork parent, which covers all of them (see
+	// permissions.Manager cascade resolution).
+	AgentNetworkProviders  Module = "agent_network.providers"
+	AgentNetworkPolicies   Module = "agent_network.policies"
+	AgentNetworkGuardrails Module = "agent_network.guardrails"
+	AgentNetworkBudgets    Module = "agent_network.budgets"
+	AgentNetworkUsage      Module = "agent_network.usage"
+	AgentNetworkLogs       Module = "agent_network.logs"
+	AgentNetworkSettings   Module = "agent_network.settings"
 )
 
 var All = map[Module]struct{}{
@@ -40,4 +53,21 @@ var All = map[Module]struct{}{
 	IdentityProviders: {},
 	Services:          {},
 	AgentNetwork:      {},
+
+	AgentNetworkProviders:  {},
+	AgentNetworkPolicies:   {},
+	AgentNetworkGuardrails: {},
+	AgentNetworkBudgets:    {},
+	AgentNetworkUsage:      {},
+	AgentNetworkLogs:       {},
+	AgentNetworkSettings:   {},
+}
+
+// Parent returns the module owning a dotted submodule name and true, or the
+// module itself and false when it has no parent.
+func (m Module) Parent() (Module, bool) {
+	if i := strings.IndexByte(string(m), '.'); i > 0 {
+		return Module(string(m)[:i]), true
+	}
+	return m, false
 }