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/IdentityManager.tsx

@@ -42,7 +42,7 @@ export default function IdentityManager({
         </button>
       </div>
 
-      <div className="flex-1 space-y-2 pr-2 -mr-2 overflow-y-auto max-h-[400px] scrollbar-thin scrollbar-thumb-slate-800 scrollbar-track-transparent">
+      <div className="flex-1 space-y-1.5 pr-2 -mr-2 overflow-y-auto max-h-[400px] scrollbar-thin scrollbar-thumb-slate-800 scrollbar-track-transparent">
         {users.map((user) => (
           <div key={user.id} className="flex items-center justify-between p-3.5 bg-background/40 border border-slate-800/40 rounded-2xl hover:border-primary/30 transition-all group">
             <div className="flex items-center gap-3 min-w-0">
@@ -98,32 +98,32 @@ export default function IdentityManager({
               </button>
             </div>
             
-            <div className="space-y-4">
-              <div className="space-y-1.5">
+            <div className="space-y-3">
+              <div className="space-y-1">
                 <label className="text-sm font-normal text-secondary tracking-tight ml-1">Username</label>
-                <input 
-                  type="text" 
+                <input
+                  type="text"
                   value={editUserForm.username}
                   onChange={(e) => setEditUserForm({ ...editUserForm, username: e.target.value })}
-                  className="w-full bg-background/80 border border-slate-800 rounded-2xl py-3 px-4 text-sm font-normal text-white outline-none focus:border-primary/50 focus-visible:ring-2 focus-visible:ring-primary focus-visible:ring-offset-0 transition-all font-mono"
+                  className="w-full bg-background/80 border border-slate-800 rounded-2xl py-2 px-4 text-sm font-normal text-white outline-none focus:border-primary/50 focus-visible:ring-2 focus-visible:ring-primary focus-visible:ring-offset-0 transition-all font-mono"
                 />
               </div>
-              <div className="space-y-1.5">
+              <div className="space-y-1">
                 <label className="text-sm font-normal text-secondary tracking-tight ml-1">New Password (Leave Empty To Keep)</label>
-                <input 
-                  type="password" 
+                <input
+                  type="password"
                   value={editUserForm.password}
                   onChange={(e) => setEditUserForm({ ...editUserForm, password: e.target.value })}
                   placeholder="********"
-                  className="w-full bg-background/80 border border-slate-800 rounded-2xl py-3 px-4 text-sm font-normal text-white outline-none focus:border-primary/50 focus-visible:ring-2 focus-visible:ring-primary focus-visible:ring-offset-0 transition-all font-mono"
+                  className="w-full bg-background/80 border border-slate-800 rounded-2xl py-2 px-4 text-sm font-normal text-white outline-none focus:border-primary/50 focus-visible:ring-2 focus-visible:ring-primary focus-visible:ring-offset-0 transition-all font-mono"
                 />
               </div>
-              <div className="space-y-1.5">
+              <div className="space-y-1">
                 <label className="text-sm font-normal text-secondary tracking-tight ml-1">Role</label>
-                <select 
+                <select
                   value={editUserForm.role}
                   onChange={(e) => setEditUserForm({ ...editUserForm, role: e.target.value })}
-                  className="w-full bg-background/80 border border-slate-800 rounded-2xl py-3 px-4 text-sm font-normal text-white outline-none focus:border-primary/50 transition-all appearance-none"
+                  className="w-full bg-background/80 border border-slate-800 rounded-2xl py-2 px-4 text-sm font-normal text-white outline-none focus:border-primary/50 transition-all appearance-none"
                 >
                   <option value="user">Standard User</option>
                   <option value="admin">Administrator</option>