feat: support multiple canvas_types for agent templates and remove duplicate files (#14030)

### What problem does this PR solve?

Closes #13907

The template catalog had duplicate files (e.g. `*_r.json`) only to place
the same template into multiple sidebar groups.
This increases maintenance cost and makes template updates error-prone.

This PR adds first-class support for multiple template categories in a
single file via `canvas_types`, then removes duplicate template files.

What changed:
- Added `canvas_types` to `CanvasTemplate` model and DB migration.
- Added normalization logic when loading templates:
  - accepts legacy `canvas_type`
  - accepts new `canvas_types`
  - merges/deduplicates values
- preserves backward compatibility by keeping `canvas_type` as first
normalized value.
- Updated template import flow to load only `.json` files and in stable
sorted order.
- Updated frontend template filtering to match on `canvas_types` first,
with fallback to legacy `canvas_type`.
- Consolidated duplicated template pairs into single files and removed:
  - `deep_search_r.json`
  - `reflective_academic_paper_generator_r.json`
  - `seo_article_writer_r.json`
- Added regression/edge-case tests for category normalization and route
serialization expectations.

### Type of change

- [ ] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)
- [ ] Documentation Update
- [ ] Refactoring
- [ ] Performance Improvement
- [ ] Other (please describe):

web/src/interfaces/database/agent.ts

@@ -87,6 +87,7 @@ export declare interface IFlow {
 export interface IFlowTemplate {
   avatar: string;
   canvas_type: string;
+  canvas_types?: string[];
   create_date: string;
   create_time: number;
   canvas_category?: string;