feat(presets): admin preset stories (premade example videos) end-to-end

Epic A — admins author premade example videos per template; users pick one
on the template detail page to start a pre-filled project.

Backend (content-svc):
- PresetStory DTOs + PresetStoryService (admin CRUD + public published-only
  filter via role check + soft-delete) + PresetStoriesController (/v1/preset-stories)
- DI registration; gateway route /v1/preset-stories (optionalAuth, public read)

Frontend:
- ProjectPresetStories admin authoring UI (name/description/demo upload/published/
  sort + scene picker with order+duration + advanced scenes_spa); «ویدیوهای نمونه»
  button + modal in ProjectsAdmin
- TemplateDetailExamples renders real published stories (image/video preview,
  hover → "use this example" → creates a pre-bound project), falls back to
  placeholders when none; selected aspect's variant id keys the fetch
- public /api/preset-stories route; preset_story_id plumbed through
  createProjectFromTemplate + projects POST route; usePreset i18n (fa+en)

Verified: full CRUD via gateway (public hides unpublished); creating a project
with presetStoryId persists selected_preset_story_id on the saved project.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/content/FlatRender.ContentSvc/Application/Services/PresetStoryService.cs

@@ -0,0 +1,99 @@
+using FlatRender.ContentSvc.Domain.Entities;
+using FlatRender.ContentSvc.Infrastructure.Data;
+using FlatRender.ContentSvc.Models;
+using Microsoft.EntityFrameworkCore;
+
+namespace FlatRender.ContentSvc.Application.Services;
+
+/// <summary>
+/// CRUD for admin-authored preset stories (premade example videos) per template.
+/// Public callers see published stories only; admins see drafts too.
+/// </summary>
+public class PresetStoryService(ContentDbContext db)
+{
+    public async Task<List<PresetStorySummary>> GetByProjectAsync(Guid projectId, bool publishedOnly) =>
+        await db.PresetStories
+            .Where(s => s.ProjectId == projectId && (!publishedOnly || s.IsPublished))
+            .OrderBy(s => s.Sort).ThenByDescending(s => s.CreatedAt)
+            .Select(s => new PresetStorySummary(
+                s.Id, s.ProjectId, s.Name, s.Description, s.Demo, s.MusicId,
+                s.Sort, s.IsPublished, s.Scenes.Count, s.CreatedAt, s.UpdatedAt))
+            .ToListAsync();
+
+    public async Task<PresetStoryResponse?> GetAsync(Guid id, bool publishedOnly)
+    {
+        var s = await db.PresetStories
+            .Include(x => x.Scenes).ThenInclude(ps => ps.Scene)
+            .FirstOrDefaultAsync(x => x.Id == id);
+        if (s == null || (publishedOnly && !s.IsPublished)) return null;
+        return ToResponse(s);
+    }
+
+    public async Task<PresetStoryResponse> CreateAsync(SavePresetStoryRequest req)
+    {
+        var story = new PresetStory
+        {
+            ProjectId = req.ProjectId,
+            Name = req.Name,
+            Description = req.Description,
+            Demo = req.Demo,
+            MusicId = req.MusicId,
+            ScenesSpa = req.ScenesSpa,
+            Sort = req.Sort,
+            IsPublished = req.IsPublished,
+            Scenes = MapScenes(req.Scenes),
+        };
+        db.PresetStories.Add(story);
+        await db.SaveChangesAsync();
+        return await ReloadAsync(story.Id);
+    }
+
+    public async Task<PresetStoryResponse> UpdateAsync(Guid id, SavePresetStoryRequest req)
+    {
+        var story = await db.PresetStories.Include(s => s.Scenes).FirstOrDefaultAsync(s => s.Id == id)
+            ?? throw new KeyNotFoundException($"Preset story {id} not found");
+        story.Name = req.Name;
+        story.Description = req.Description;
+        story.Demo = req.Demo;
+        story.MusicId = req.MusicId;
+        if (req.ScenesSpa != null) story.ScenesSpa = req.ScenesSpa;
+        story.Sort = req.Sort;
+        story.IsPublished = req.IsPublished;
+        story.UpdatedAt = DateTime.UtcNow;
+        // Replace the scene set wholesale (small, ordered list).
+        if (req.Scenes != null)
+        {
+            db.PresetScenes.RemoveRange(story.Scenes);
+            story.Scenes = MapScenes(req.Scenes);
+        }
+        await db.SaveChangesAsync();
+        return await ReloadAsync(story.Id);
+    }
+
+    public async Task DeleteAsync(Guid id)
+    {
+        var story = await db.PresetStories.FirstOrDefaultAsync(s => s.Id == id)
+            ?? throw new KeyNotFoundException($"Preset story {id} not found");
+        story.DeletedAt = DateTime.UtcNow; // soft delete (global query filter hides it)
+        await db.SaveChangesAsync();
+    }
+
+    // ── helpers ───────────────────────────────────────────────────────────────
+    private static List<PresetScene> MapScenes(List<PresetSceneInput>? scenes) =>
+        (scenes ?? []).Select(s => new PresetScene
+        {
+            SceneId = s.SceneId,
+            Sort = s.Sort,
+            DefaultDurationSec = s.DefaultDurationSec,
+        }).ToList();
+
+    private async Task<PresetStoryResponse> ReloadAsync(Guid id) =>
+        ToResponse(await db.PresetStories.Include(x => x.Scenes).ThenInclude(ps => ps.Scene)
+            .FirstAsync(x => x.Id == id));
+
+    private static PresetStoryResponse ToResponse(PresetStory s) => new(
+        s.Id, s.ProjectId, s.Name, s.Description, s.Demo, s.MusicId, s.ScenesSpa,
+        s.Sort, s.IsPublished, s.CreatedAt, s.UpdatedAt,
+        s.Scenes.OrderBy(ps => ps.Sort).Select(ps => new PresetSceneResponse(
+            ps.Id, ps.SceneId, ps.Scene?.Key, ps.Scene?.Title, ps.Sort, ps.DefaultDurationSec)).ToList());
+}