fix: resolve all frontend lint errors and warnings

Replace all `any` types with proper types across 36 files:
- TanStack Router search params: `{} as Record<string, unknown>`
- API response pagination: proper typed interface
- DataTable column casts: remove unnecessary `as any`
- Function params and event handlers: use specific types
- Remove unused imports and variables in POS components

Frontend lint now passes with 0 errors and 0 warnings.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/admin/src/routes/_authenticated/lessons/sessions/index.tsx

@@ -92,13 +92,13 @@ function SessionsPage() {
   const weekEnd = endOfWeek(weekStart, { weekStartsOn: 0 })
 
   function setView(v: 'list' | 'week') {
-    navigate({ to: '/lessons/sessions', search: { ...search, view: v, page: 1 } as any })
+    navigate({ to: '/lessons/sessions', search: { ...search, view: v, page: 1 } as Record<string, unknown> })
   }
 
   function handleStatusChange(v: string) {
     const s = v === 'all' ? '' : v
     setStatusFilter(s)
-    navigate({ to: '/lessons/sessions', search: { ...search, status: s || undefined, page: 1 } as any })
+    navigate({ to: '/lessons/sessions', search: { ...search, status: s || undefined, page: 1 } as Record<string, unknown> })
   }
 
   // List query
@@ -189,7 +189,7 @@ function SessionsPage() {
             order={params.order}
             onPageChange={setPage}
             onSort={setSort}
-            onRowClick={(s) => navigate({ to: '/lessons/sessions/$sessionId', params: { sessionId: s.id }, search: {} as any })}
+            onRowClick={(s) => navigate({ to: '/lessons/sessions/$sessionId', params: { sessionId: s.id }, search: {} as Record<string, unknown> })}
           />
         </>
       )}
@@ -249,7 +249,7 @@ function SessionsPage() {
                   {daySessions.map((s) => (
                     <button
                       key={s.id}
-                      onClick={() => navigate({ to: '/lessons/sessions/$sessionId', params: { sessionId: s.id }, search: {} as any })}
+                      onClick={() => navigate({ to: '/lessons/sessions/$sessionId', params: { sessionId: s.id }, search: {} as Record<string, unknown> })}
                       className={`w-full text-left rounded border px-1.5 py-1 text-xs hover:opacity-80 transition-opacity ${STATUS_COLORS[s.status] ?? STATUS_COLORS.scheduled}`}
                     >
                       <p className="font-semibold">{formatTime(s.scheduledTime)}</p>