feat: Public-Flag für Agents + verfügbare Agents/Bots Endpoints erweitert

- AgentRecord: neues IsPublic-Feld mit DB-Migration
- GET /api/agents/available: eigene + public Agents (alle Properties + isOwner)
- GET /api/telegram/bots/available: alle Properties außer Token/Secret + sessionCount
- Agent-Page: Public-Checkbox (andere User können Agent in Sessions verwenden)
- Dashboard: agentMap aus availableAgents gebaut (public Agents fremder User auflösbar)
- Session-Page + Cronjob-Page: Agent-Picker nutzt /available statt /agents
- Agent-Cards: Public- und Fremd-Badges
- Fix: Chat-Button bei Sessions mit public Agent eines anderen Users nicht mehr disabled

Services/DatabaseService.cs

@@ -284,6 +284,7 @@ public class DatabaseService
         ");
 
         TryAddColumn(conn, "agents", "avatar_small", "TEXT");
+        TryAddColumn(conn, "agents", "is_public", "INTEGER NOT NULL DEFAULT 0");
         TryAddColumn(conn, "sessions", "image_small", "TEXT");
 
         // Migration: Bestehende PNG/JPEG-Avatare/Images zu WebP konvertieren
@@ -499,6 +500,13 @@ public class DatabaseService
             "SELECT * FROM agents WHERE user_id = @userId AND is_deleted = 0 ORDER BY name", new { userId });
     }
 
+    public async Task<IEnumerable<AgentRecord>> GetAvailableAgents(string userId)
+    {
+        using var conn = CreateConnection();
+        return await conn.QueryAsync<AgentRecord>(
+            "SELECT * FROM agents WHERE (user_id = @userId OR is_public = 1) AND is_deleted = 0 ORDER BY name", new { userId });
+    }
+
     public async Task<AgentRecord> GetAgent(string agentId)
     {
         using var conn = CreateConnection();
@@ -516,7 +524,8 @@ public class DatabaseService
                 custom_commands = @CustomCommands, auto_commit = @AutoCommit,
                 use_soul = @UseSoul, use_identity = @UseIdentity, use_user_info = @UseUserInfo, use_memory = @UseMemory, use_web_search = @UseWebSearch, web_search_version = @WebSearchVersion,
                 allow_user_choice = @AllowUserChoice, task_instruction = @TaskInstruction,
-                avatar_scale = @AvatarScale, avatar_offset_x = @AvatarOffsetX, avatar_offset_y = @AvatarOffsetY, updated_at = @UpdatedAt
+                avatar_scale = @AvatarScale, avatar_offset_x = @AvatarOffsetX, avatar_offset_y = @AvatarOffsetY,
+                is_public = @IsPublic, updated_at = @UpdatedAt
             WHERE agent_id = @AgentId AND user_id = @UserId
         ", agent);
     }