docs: update API documentation for consolidated user management

Add documentation for delete_user and reset_user_password endpoints.
Update update_profile to reflect consolidated endpoint. Remove obsolete
documentation for individual update operations. Add profile guide for
end-users. Update API_CONSOLIDATION_PLAN.md with implementation status.

docs/user/profile-guide.md

@@ -0,0 +1,98 @@
+# Profile Management Guide
+
+## Updating Your Profile
+
+Your profile contains your account information and preferences.
+
+### How to Update
+
+1. Click on your **username** (top-right)
+2. Select **Profile** from the dropdown
+3. Edit any fields in the "Account Information" section
+4. Click **Update Profile**
+5. Changes take effect immediately
+
+### Fields You Can Update
+
+- **Username** - Your login name (must be unique)
+- **Email** - Your email address (must be unique)
+- **First Name** - Optional display name
+- **Last Name** - Optional display name
+- **Theme** - Your preferred color scheme
+
+## Changing Your Password
+
+Regular password changes are recommended for account security.
+
+### How to Change
+
+1. Go to **Profile** page
+2. Scroll to "Change Password" section
+3. Enter your **current password**
+4. Enter your **new password**
+5. **Confirm** your new password
+6. Click **Update Password**
+
+### Password Requirements
+
+- Minimum 8 characters
+- Must contain uppercase, lowercase, number, and special character
+- Must match confirmation field
+- Current password must be correct
+
+## Deleting Your Account
+
+**⚠️ WARNING:** This action cannot be undone.
+
+### What Gets Deleted
+
+When you delete your account:
+- Your profile information
+- Reading progress and history
+- Device connections
+- Collection preferences
+- All personal data
+
+### What Stays
+
+- Library books (media belongs to the library, not you)
+- System settings
+- Other users' accounts
+
+### How to Delete
+
+1. Go to **Profile** page
+2. Scroll to "Danger Zone" (bottom of page)
+3. Click **Remove My Account**
+4. Confirm by clicking "OK" in the popup
+
+**Note:** If you're the last admin, you cannot delete your account for security reasons.
+
+## Theme Options
+
+Personalize your reading experience with different color themes.
+
+### Quick Theme Switch
+
+1. Click the **paintbrush icon** (top-right, next to your username)
+2. Select a theme from the dropdown
+3. Changes apply instantly
+
+### Available Themes
+
+- **Tokyo Night** (default) - Blue/purple accents
+- **Dracula** - Purple/pink tones
+- **Nord** - Arctic, bluish-gray
+- **Solarized Dark** - Warm, precise contrast
+- **Monokai** - Classic vibrant colors
+- **One Dark Pro** - Atom editor inspired
+- **Material Dark** - Google Material Design
+- **Wood Light** - Light wood texture
+- **Wood Dark** - Dark wood texture  
+- **Wood Mahogany** - Reddish-brown wood
+
+## For Admin Users
+
+If you're an administrator, you can also manage other users' profiles from the admin panel.
+
+See [Admin User Management](admin-guide.md) for details.