feat: 8 AI providers, rich text editor, agent notifications, UI contrast & font settings

- Add DeepSeek, OpenRouter, Mistral, Z.AI, LM Studio as AI providers
  with editable model names via Combobox in admin settings
- Fix OpenRouter broken by normalizeProvider bug in config.ts
- Convert agent-created notes from Markdown to HTML (TipTap rich text)
- Add Notification model + in-app notifications for agent results
- Agent notification click opens the created note directly
- Add note count display on notebook and inbox headers
- Fix checklist toggle in card view (persist state via localCheckItems)
- Add checklist creation option in tabs/list view (dropdown on + button)
- Fix image description ENOENT error with HTTP fallback
- Improve UI contrast across all themes (input, border, checkbox visibility)
- Add font family setting (Inter vs System Default) in Appearance settings
- Fix CSS font-sans variable conflict (removed dead Geist references)
- Update README with new features and 8 providers

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

memento-note/components/ui/combobox.tsx

@@ -23,6 +23,8 @@ interface ComboboxProps {
   emptyMessage?: string
   disabled?: boolean
   className?: string
+  /** When true, the search text can be submitted as a custom value not in the options list */
+  allowCustomValue?: boolean
 }
 
 export function Combobox({
@@ -34,6 +36,7 @@ export function Combobox({
   emptyMessage = 'No results found.',
   disabled = false,
   className,
+  allowCustomValue = false,
 }: ComboboxProps) {
   const [open, setOpen] = React.useState(false)
   const [search, setSearch] = React.useState('')
@@ -56,6 +59,14 @@ export function Combobox({
     setSearch('')
   }
 
+  const handleConfirmCustom = () => {
+    if (allowCustomValue && search.trim()) {
+      onChange(search.trim())
+      setOpen(false)
+      setSearch('')
+    }
+  }
+
   return (
     <Popover open={open} onOpenChange={(v) => { setOpen(v); if (!v) setSearch('') }}>
       <PopoverTrigger asChild>
@@ -85,14 +96,26 @@ export function Combobox({
             placeholder={searchPlaceholder}
             value={search}
             onChange={(e) => setSearch(e.target.value)}
+            onKeyDown={(e) => { if (e.key === 'Enter') { e.preventDefault(); handleConfirmCustom() } }}
             autoFocus
           />
         </div>
         <div className="max-h-60 overflow-y-auto p-1">
           {filtered.length === 0 ? (
-            <div className="py-6 text-center text-sm text-muted-foreground">
-              {emptyMessage}
-            </div>
+            allowCustomValue && search.trim() ? (
+              <button
+                type="button"
+                onClick={handleConfirmCustom}
+                className="flex w-full cursor-pointer items-center rounded-sm px-2 py-1.5 text-sm hover:bg-accent hover:text-accent-foreground transition-colors"
+              >
+                <span className="text-muted-foreground mr-2">+</span>
+                <span>Use "<strong>{search.trim()}</strong>"</span>
+              </button>
+            ) : (
+              <div className="py-6 text-center text-sm text-muted-foreground">
+                {emptyMessage}
+              </div>
+            )
           ) : (
             filtered.map((option) => {
               const isSelected = option.value === value