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/AiManager.tsx

@@ -42,7 +42,7 @@ export default function AiManager({
         </div>
       </div>
       
-      <div className="grid sm:grid-cols-2 gap-4">
+      <div className="grid sm:grid-cols-2 gap-3">
         {aiConfig?.providers?.map((p: any) => (
           <button
             key={p.id}
@@ -83,7 +83,7 @@ export default function AiManager({
         ))}
       </div>
 
-      <div className="bg-primary/5 border border-primary/10 rounded-[2rem] p-6 space-y-6">
+      <div className="bg-primary/5 border border-primary/10 rounded-[2rem] p-6 space-y-3">
         <div className="flex items-center justify-between">
           <div className="flex items-center gap-3">
             <div className="p-2 bg-primary/10 rounded-lg text-primary"><Lock size={14} /></div>
@@ -101,7 +101,7 @@ export default function AiManager({
         </div>
 
         <div className="grid md:grid-cols-2 gap-6">
-          <div className="space-y-2">
+          <div className="space-y-1.5">
             <label className="text-sm font-normal text-secondary tracking-tight ml-1">Gemini Api Key</label>
             <div className="flex gap-2">
               <input
@@ -110,7 +110,7 @@ export default function AiManager({
                 value={aiKeys.gemini}
                 onChange={(e) => setAiKeys({...aiKeys, gemini: e.target.value})}
                 placeholder={aiConfig?.providers?.find((p: any) => p.id === 'gemini')?.masked_key || "Enter Gemini Key..."}
-                className="flex-1 bg-background/80 border border-slate-800 rounded-xl py-3 px-4 text-xs text-white outline-none focus:border-primary/50 transition-all placeholder:text-secondary"
+                className="flex-1 bg-background/80 border border-slate-800 rounded-xl py-2 px-4 text-xs text-white outline-none focus:border-primary/50 transition-all placeholder:text-secondary"
               />
               <button
                 onClick={() => onTestAiKey('gemini')}
@@ -127,7 +127,7 @@ export default function AiManager({
               </button>
             </div>
           </div>
-          <div className="space-y-2">
+          <div className="space-y-1.5">
             <label className="text-sm font-normal text-secondary tracking-tight ml-1">Claude Api Key</label>
             <div className="flex gap-2">
               <input
@@ -136,7 +136,7 @@ export default function AiManager({
                 value={aiKeys.claude}
                 onChange={(e) => setAiKeys({...aiKeys, claude: e.target.value})}
                 placeholder={aiConfig?.providers?.find((p: any) => p.id === 'claude')?.masked_key || "Enter Claude Key..."}
-                className="flex-1 bg-background/80 border border-slate-800 rounded-xl py-3 px-4 text-xs text-white outline-none focus:border-primary/50 transition-all placeholder:text-secondary"
+                className="flex-1 bg-background/80 border border-slate-800 rounded-xl py-2 px-4 text-xs text-white outline-none focus:border-primary/50 transition-all placeholder:text-secondary"
               />
               <button
                 onClick={() => onTestAiKey('claude')}
@@ -156,8 +156,8 @@ export default function AiManager({
         </div>
       </div>
 
-      <div className="space-y-4">
-        <div className="space-y-2">
+      <div className="space-y-3">
+        <div className="space-y-1.5">
           <div className="flex items-center justify-between px-1">
             <label className="text-sm font-normal text-secondary tracking-tight">System Prompt (Vision Extraction)</label>
             <button