feat: Add project filter to listInitiatives

Add findByProjectId to InitiativeRepository using a subquery on the
initiative_projects junction table. Extend the listInitiatives tRPC
procedure to accept an optional projectId filter that composes with
the existing status filter. Add a project dropdown to the initiatives
page alongside the status filter.

apps/server/trpc/routers/initiative.ts

@@ -111,12 +111,22 @@ export function initiativeProcedures(publicProcedure: ProcedureBuilder) {
     listInitiatives: publicProcedure
       .input(z.object({
         status: z.enum(['active', 'completed', 'archived']).optional(),
+        projectId: z.string().min(1).optional(),
       }).optional())
       .query(async ({ ctx, input }) => {
         const repo = requireInitiativeRepository(ctx);
-        const initiatives = input?.status
-          ? await repo.findByStatus(input.status)
-          : await repo.findAll();
+
+        let initiatives;
+        if (input?.projectId) {
+          const all = await repo.findByProjectId(input.projectId);
+          initiatives = input.status
+            ? all.filter(i => i.status === input.status)
+            : all;
+        } else {
+          initiatives = input?.status
+            ? await repo.findByStatus(input.status)
+            : await repo.findAll();
+        }
 
         // Fetch active architect agents once for all initiatives
         const ARCHITECT_MODES = ['discuss', 'plan', 'detail', 'refine'];