feat: Add merge conflict detection and agent resolution in initiative review

Pre-merge mergeability check via `git merge-tree --write-tree` (dry-run, no
side effects). When conflicts exist the "Merge & Push" button is disabled and
a ConflictResolutionPanel shows conflict files with options to resolve manually
or spawn a conflict-resolution agent. Agent questions appear inline via
QuestionForm; on completion the mergeability re-checks automatically.

New server-side: MergeabilityResult type, BranchManager.checkMergeability,
conflict-resolution prompt, checkInitiativeMergeability query,
spawnConflictResolutionAgent mutation, getActiveConflictAgent query.

New frontend: useConflictAgent hook, ConflictResolutionPanel component,
mergeability badge + panel integration in InitiativeReview.

apps/server/trpc/routers/agent.ts

@@ -184,6 +184,27 @@ export function agentProcedures(publicProcedure: ProcedureBuilder) {
         return candidates[0] ?? null;
       }),
 
+    getActiveConflictAgent: publicProcedure
+      .input(z.object({ initiativeId: z.string().min(1) }))
+      .query(async ({ ctx, input }): Promise<AgentInfo | null> => {
+        const agentManager = requireAgentManager(ctx);
+        const allAgents = await agentManager.list();
+        const candidates = allAgents
+          .filter(
+            (a) =>
+              a.mode === 'execute' &&
+              a.initiativeId === input.initiativeId &&
+              a.name?.startsWith('conflict-') &&
+              ['running', 'waiting_for_input', 'idle', 'crashed'].includes(a.status) &&
+              !a.userDismissedAt,
+          )
+          .sort(
+            (a, b) =>
+              new Date(b.createdAt).getTime() - new Date(a.createdAt).getTime(),
+          );
+        return candidates[0] ?? null;
+      }),
+
     getAgentOutput: publicProcedure
       .input(agentIdentifierSchema)
       .query(async ({ ctx, input }): Promise<string> => {