fix: implement Phase 2 medium-impact spacing reductions

Applied systematic spacing optimizations across admin manager components (40px savings):

DatabaseManager.tsx:
- Input field padding: py-3 → py-2 (3 inputs: retention_count, schedule_hour, schedule_freq_days)
- Form field spacing: space-y-2 → space-y-1.5 (Max Backups field group)
- Grid gaps: gap-4 → gap-3 (storage policy fields)
- Item list spacing: space-y-2 → space-y-1.5 (backup list)
- Modal form spacing: space-y-4 → space-y-3 (recovery points section)
- Backup metadata text: text-[11px] → text-xs (created_at + filesize display)

LdapManager.tsx:
- Input field padding: py-2.5 → py-2 (4 inputs: server_uri, base_dn, user_template, groups_dn)
- Form field spacing: space-y-1.5 → space-y-1 (all label+input groups)
- Button padding: py-2.5 → py-2 (test connection), py-3 → py-2.5 (save policy)

IdentityManager.tsx:
- Input field padding: py-3 → py-2 (username, password, role in edit modal)
- Form field spacing: space-y-4 → space-y-3 (edit modal form)
- Form field labels: space-y-1.5 → space-y-1 (all 3 fields)
- User list spacing: space-y-2 → space-y-1.5 (user items)

AiManager.tsx:
- Grid gaps: gap-4 → gap-3 (provider options grid)
- Input field padding: py-3 → py-2 (Gemini/Claude API key inputs)
- Form field spacing: space-y-2 → space-y-1.5 (API key field groups)
- Modal spacing: space-y-6 → space-y-3 (provider access keys section)
- Prompt section spacing: space-y-4 → space-y-3 (system prompt area)

CategoryManager.tsx:
- Grid gaps: gap-3 → gap-2.5 (category items grid)
- Input field padding: py-3.5 → py-2.5, py-4 → py-2.5 (name + description inputs)
- Form field spacing: space-y-6 → space-y-3, space-y-1.5 → space-y-1 (edit modal)

Test Results:
- Frontend (Vitest): 291/291 tests passing ✓
- Backend (Pytest): 41/41 tests passing ✓
- Total: 332 tests validated, zero regressions

All changes maintain visual hierarchy and premium density standards without sacrificing usability.

frontend/components/admin/CategoryManager.tsx

@@ -40,7 +40,7 @@ export default function CategoryManager({
           </button>
       </div>
 
-      <div data-testid="category-list" className="grid sm:grid-cols-2 lg:grid-cols-4 gap-3">
+      <div data-testid="category-list" className="grid sm:grid-cols-2 lg:grid-cols-4 gap-2.5">
          {categories.map(cat => (
            <div key={cat.id} data-testid="category-item" className="p-4 bg-background/40 border border-slate-800/50 rounded-2xl flex items-center justify-between group hover:border-primary/40 transition-all">
              <div className="min-w-0 pr-4">
@@ -84,23 +84,23 @@ export default function CategoryManager({
                  <X size={20} />
                </button>
             </div>
-            <div data-testid="category-form" className="space-y-6">
-               <div className="space-y-1.5">
+            <div data-testid="category-form" className="space-y-3">
+               <div className="space-y-1">
                   <label className="text-sm font-normal text-secondary tracking-tight ml-1">Group Identifier</label>
                   <input
                     data-testid="category-name-input"
                     type="text"
                     value={editCatForm.name}
                     onChange={(e) => setEditCatForm({...editCatForm, name: e.target.value})}
-                    className="w-full bg-background border border-slate-800 rounded-2xl py-3.5 px-5 text-sm text-white focus:border-primary outline-none transition-all"
+                    className="w-full bg-background border border-slate-800 rounded-2xl py-2.5 px-5 text-sm text-white focus:border-primary outline-none transition-all"
                   />
                </div>
-               <div className="space-y-1.5">
+               <div className="space-y-1">
                   <label className="text-sm font-normal text-secondary tracking-tight ml-1">Strategic Description</label>
-                  <textarea 
+                  <textarea
                     value={editCatForm.description}
                     onChange={(e) => setEditCatForm({...editCatForm, description: e.target.value})}
-                    className="w-full bg-background border border-slate-800 rounded-2xl py-4 px-5 text-sm text-white focus:border-primary outline-none transition-all h-32 resize-none"
+                    className="w-full bg-background border border-slate-800 rounded-2xl py-2.5 px-5 text-sm text-white focus:border-primary outline-none transition-all h-32 resize-none"
                   />
                </div>
                <button data-testid="add-category-submit" onClick={onUpdateCategorySubmit} className="w-full bg-primary hover:bg-primary text-white font-normal py-4 rounded-2xl shadow-xl shadow-primary/20 active:scale-95 transition-all text-sm mb-4 tracking-tight">