feat: add web bookmark creation (NIP-B0, kind:39701)

- Created webBookmarkService for creating web bookmarks
- Added AddBookmarkModal component with URL, title, and description fields
- Added plus button to sidebar header (visible when logged in)
- Modal validates URL format and publishes to relays
- Auto-refreshes bookmarks after creation
- Styled modal with dark theme matching app design
- Follows NIP-B0 spec: URL in 'd' tag, title and summary tags

src/components/AddBookmarkModal.tsx

@@ -0,0 +1,131 @@
+import React, { useState } from 'react'
+import { FontAwesomeIcon } from '@fortawesome/react-fontawesome'
+import { faTimes } from '@fortawesome/free-solid-svg-icons'
+import IconButton from './IconButton'
+
+interface AddBookmarkModalProps {
+  onClose: () => void
+  onSave: (url: string, title?: string, description?: string) => Promise<void>
+}
+
+const AddBookmarkModal: React.FC<AddBookmarkModalProps> = ({ onClose, onSave }) => {
+  const [url, setUrl] = useState('')
+  const [title, setTitle] = useState('')
+  const [description, setDescription] = useState('')
+  const [isSaving, setIsSaving] = useState(false)
+  const [error, setError] = useState<string | null>(null)
+
+  const handleSubmit = async (e: React.FormEvent) => {
+    e.preventDefault()
+    setError(null)
+
+    if (!url.trim()) {
+      setError('URL is required')
+      return
+    }
+
+    // Validate URL
+    try {
+      new URL(url)
+    } catch {
+      setError('Please enter a valid URL')
+      return
+    }
+
+    try {
+      setIsSaving(true)
+      await onSave(
+        url.trim(),
+        title.trim() || undefined,
+        description.trim() || undefined
+      )
+      onClose()
+    } catch (err) {
+      console.error('Failed to save bookmark:', err)
+      setError(err instanceof Error ? err.message : 'Failed to save bookmark')
+    } finally {
+      setIsSaving(false)
+    }
+  }
+
+  return (
+    <div className="modal-overlay" onClick={onClose}>
+      <div className="modal-content" onClick={(e) => e.stopPropagation()}>
+        <div className="modal-header">
+          <h2>Add Bookmark</h2>
+          <IconButton
+            icon={faTimes}
+            onClick={onClose}
+            title="Close"
+            ariaLabel="Close modal"
+            variant="ghost"
+          />
+        </div>
+
+        <form onSubmit={handleSubmit} className="modal-form">
+          <div className="form-group">
+            <label htmlFor="bookmark-url">URL *</label>
+            <input
+              id="bookmark-url"
+              type="text"
+              value={url}
+              onChange={(e) => setUrl(e.target.value)}
+              placeholder="https://example.com"
+              disabled={isSaving}
+              autoFocus
+            />
+          </div>
+
+          <div className="form-group">
+            <label htmlFor="bookmark-title">Title</label>
+            <input
+              id="bookmark-title"
+              type="text"
+              value={title}
+              onChange={(e) => setTitle(e.target.value)}
+              placeholder="Optional title"
+              disabled={isSaving}
+            />
+          </div>
+
+          <div className="form-group">
+            <label htmlFor="bookmark-description">Description</label>
+            <textarea
+              id="bookmark-description"
+              value={description}
+              onChange={(e) => setDescription(e.target.value)}
+              placeholder="Optional description"
+              disabled={isSaving}
+              rows={3}
+            />
+          </div>
+
+          {error && (
+            <div className="modal-error">{error}</div>
+          )}
+
+          <div className="modal-actions">
+            <button
+              type="button"
+              onClick={onClose}
+              className="btn-secondary"
+              disabled={isSaving}
+            >
+              Cancel
+            </button>
+            <button
+              type="submit"
+              className="btn-primary"
+              disabled={isSaving}
+            >
+              {isSaving ? 'Saving...' : 'Save Bookmark'}
+            </button>
+          </div>
+        </form>
+      </div>
+    </div>
+  )
+}
+
+export default AddBookmarkModal
+