feat(P5): IHF Phase 5 complete — agent-assisted distillation

Adds bounded AI support to the IHF governance loop. All AI outputs are
attributed (model_ref), reviewable (AgentReviewRecord), and reversible.
No autonomous decisions; no silent requirement promotion.

- T01: Schema — agent_proposals, agent_review_records,
  confidence_annotations (migration 1743379200)
- T02: AgentProposalsController (index/show/accept/reject, idempotent
  review guard), global nav "Agent" link
- T03: SummarizeClusterAction — Claude API cluster summary on widget show
- T04: DraftRequirementAction — AI requirement draft; acceptance creates
  RequirementCandidate (human-gated)
- T05: DetectDuplicatesAction — duplicate_flag proposal on candidate show
- T06: DetectPolicySensitivityAction — policy_flag with
  ConfidenceAnnotations per concern scope
- T07: ProposeImplementationAction — impl_proposal from decision show
- T08: AgentAuditDashboardAction — autoRefresh; KPI row, unreviewed queue,
  recent proposals, attribution log matrix
- T09: integration tests, SCOPE.md updated, phase5-summary.md, flake.nix
  adds http-conduit/aeson/string-conversions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Web/FrontController.hs

@@ -16,6 +16,7 @@ import Web.Controller.RequirementCandidates ()
 import Web.Controller.Requirements ()
 import Web.Controller.DecisionRecords ()
 import Web.Controller.DeploymentRecords ()
+import Web.Controller.AgentProposals ()
 import Web.Controller.Sessions ()
 
 instance FrontController WebApplication where
@@ -30,6 +31,7 @@ instance FrontController WebApplication where
         , parseRoute @RequirementsController
         , parseRoute @DecisionRecordsController
         , parseRoute @DeploymentRecordsController
+        , parseRoute @AgentProposalsController
         ]
 
 instance InitControllerContext WebApplication where
@@ -59,6 +61,7 @@ defaultLayout inner = [hsx|
                 <a href={RequirementsAction} class="text-sm text-gray-600 hover:text-gray-900">Requirements</a>
                 <a href={DecisionRecordsAction} class="text-sm text-gray-600 hover:text-gray-900">Decisions</a>
                 <a href={DeploymentRecordsAction} class="text-sm text-gray-600 hover:text-gray-900">Deployments</a>
+                <a href={AgentProposalsAction} class="text-sm text-gray-600 hover:text-gray-900">Agent</a>
                 <div class="ml-auto">
                     <a href={DeleteSessionAction} class="text-sm text-gray-500 hover:text-gray-700">Sign out</a>
                 </div>