docs: enhance auto sync documentation with frontmatter key configuration and examples

docs/en/03-configuration.md

@@ -22,6 +22,21 @@ In the plugin settings, you can add and configure the Notion databases you want
   - [3️⃣ Custom Database](#3️⃣-custom-database)
   - [Finalizing Configuration](#finalizing-configuration)
 
+## Auto Sync Frontmatter Entry
+
+If you enable auto sync, the plugin needs a frontmatter entry that lists which configured databases should receive updates. You can customise the name of this entry in **Settings → Auto Sync Frontmatter Key** (default: `autosync-database`). Use any text you like—letters, numbers, emojis, or other scripts are all supported.
+
+In your note's frontmatter, add the configured key and list the database abbreviations you created in the settings:
+
+```yaml
+---
+title: My Article
+autosync-database: [blog, ideas]
+---
+```
+
+The entry can be a YAML list or comma-separated string, and manual uploads will automatically add the current database abbreviation if it is missing. If you change the key name in settings, update your frontmatter to match the new value.
+
 ## 1️⃣ General Database
 
 This is the most basic database type and is suitable for most users.
@@ -109,4 +124,4 @@ Relation and Rollup types are not supported yet.
 
 ## Finalizing Configuration
 
-After configuring your database, make sure to save your settings. You can now start syncing your Obsidian notes to the configured Notion database by using the "Share to NotionNext" command from the command palette or the note context menu.
+After configuring your database, make sure to save your settings. You can now start syncing your Obsidian notes to the configured Notion database by using the "Share to NotionNext" command from the command palette or the note context menu.

docs/en/04-sync.md

@@ -22,6 +22,25 @@ The plugin supports automatic syncing that monitors your notes for changes and a
 3. Enable the toggle
 4. Configure the "Auto Sync Delay" (default: 5 seconds, minimum: 2 seconds)
 
+### Prepare the Frontmatter
+
+Auto sync reads the database list from the frontmatter key you configured in **Settings → Auto Sync Frontmatter Key** (default: `autosync-database`). To make sure your notes can sync automatically:
+
+- Add the configured key to your note's frontmatter
+- List one or more database abbreviations that you defined in the plugin settings
+- Keep the list updated if you change the databases a note should sync to
+
+Example with the default key:
+
+```yaml
+---
+title: My Article
+autosync-database: [blog, portfolio]
+---
+```
+
+If you change the key name in the settings, update your frontmatter to match. The plugin will prompt you when the entry is missing.
+
 ### How Auto Sync Works
 
 When auto sync is enabled:
@@ -32,7 +51,7 @@ When auto sync is enabled:
 
 ### Auto Sync Scenarios
 
-#### Scenario A: New Document (Not Yet Synced)
+#### Scenario A: Missing Auto Sync Entry
 
 ```yaml
 ---
@@ -41,18 +60,34 @@ tags: [blog, tech]
 ---
 ```
 
+**Behavior:**
+- ✅ Detects that the configured auto sync key is missing
+- ✅ Shows notice: `⚠️ Auto sync skipped: Add a "{key}" entry in the frontmatter to choose databases`
+- ✅ No sync operation performed
+- 📝 **Action Required:** Add the configured key (default `autosync-database`) to the frontmatter with the database abbreviations
+
+#### Scenario B: New Document (Not Yet Synced)
+
+```yaml
+---
+title: My New Article
+aytosync-database: [blog]
+---
+```
+
 **Behavior:**
 - ✅ Detects no NotionID present
 - ✅ Shows notice: "⚠️ Auto sync skipped: This document has not been synced to Notion, please upload manually first"
 - ✅ No sync operation performed
 - 📝 **Action Required:** Manually sync the document first using the command palette
 
-#### Scenario B: Synced to One Database
+#### Scenario C: Synced to One Database
 
 ```yaml
 ---
 title: My Article
 NotionID-blog: abc123
+autosync-database: [blog]
 ---
 ```
 
@@ -62,7 +97,7 @@ NotionID-blog: abc123
 - ✅ Shows success/failure notification from the upload command
 - 📝 **No Action Required:** Changes are automatically synced
 
-#### Scenario C: Synced to Multiple Databases
+#### Scenario D: Synced to Multiple Databases
 
 ```yaml
 ---
@@ -80,6 +115,21 @@ NotionID-notes: ghi789
 - ✅ Shows individual result notifications for each database
 - 📝 **No Action Required:** Changes are automatically synced to all linked databases
 
+#### Scenario E: Custom Frontmatter Key
+
+```yaml
+---
+title: My Article
+NotionID-blog: abc123
+NotionID-portfolio: def456
+🚀-sync-targets: [blog, portfolio]
+---
+```
+
+**Behavior:**
+- ✅ Uses your custom key (for example `🚀-sync-targets`) configured in settings
+- ✅ Syncs to the listed databases when NotionIDs are present
+- 📝 **Remember:** Update both the setting and your frontmatter if you rename the key
 ### Auto Sync Best Practices
 
 1. **First Sync Manually**: Always perform the first sync manually to establish the NotionID link