feat(canvas): build PSD export in the browser from canvas layers

Move PSD generation off the server. The image-generation API only
produces raster formats, so drop the PSD request path, the oov/psd
decoder, and the LayeredDocumentGenerator wiring. Layer separation now
returns clean background, foreground, and text_render_data artifacts
into a transparent frame.

Export that frame (or any image node) as PSD from the canvas context
menu: ag-psd assembles layers, rotation/flip, opacity, editable text,
and stroke effects from the current canvas state at download time.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/pnpm-lock.yaml

@@ -23,6 +23,9 @@ dependencies:
   '@radix-ui/react-tabs':
     specifier: ^1.1.16
     version: 1.1.16(@types/react-dom@19.2.3)(@types/react@19.2.17)(react-dom@19.2.7)(react@19.2.7)
+  ag-psd:
+    specifier: 31.0.2
+    version: 31.0.2
   lucide-react:
     specifier: ^1.23.0
     version: 1.23.0(react@19.2.7)
@@ -1246,6 +1249,13 @@ packages:
       vite: 8.1.3(@types/node@26.1.0)
     dev: true
 
+  /ag-psd@31.0.2:
+    resolution: {integrity: sha512-5s5PvqbomPIIJ9YjL6robz55rT4RYPiQkww4brisyZEb5jzlHB1EKh47IJg7gIFj0RUrD0cMgdntM907qaZjXA==}
+    dependencies:
+      base64-js: 1.5.1
+      pako: 2.1.0
+    dev: false
+
   /aria-hidden@1.2.6:
     resolution: {integrity: sha512-ik3ZgC9dY/lYVVM++OISsaYDeg1tb0VtP5uL3ouh1koGOaUMDPpbFIei4JkFimWUFPn90sbMNMXQAIVOlnYKJA==}
     engines: {node: '>=10'}
@@ -1253,6 +1263,10 @@ packages:
       tslib: 2.8.1
     dev: false
 
+  /base64-js@1.5.1:
+    resolution: {integrity: sha512-AKpaYlHn8t4SVbOHCy+b5+KKgvR4vrsD8vbvrbiQJps7fKDTkjkDry6ji0rUJjC0kzbNePLwzxq8iypo41qeWA==}
+    dev: false
+
   /baseline-browser-mapping@2.10.41:
     resolution: {integrity: sha512-WwS7MHhqGHHlaVsqRZnhvCEMS0owDX+SxRlve7JkuH7My1Ara3ZriTmCQupPfYjxMZ8I/tgxtJYr2t7taHaH4A==}
     engines: {node: '>=6.0.0'}
@@ -1482,6 +1496,10 @@ packages:
       - babel-plugin-macros
     dev: false
 
+  /pako@2.1.0:
+    resolution: {integrity: sha512-w+eufiZ1WuJYgPXbV/PO3NCMEc3xqylkKHzp8bxp1uW4qaSNQUkwmLLEc3kKsfz8lpV1F8Ht3U1Cm+9Srog2ug==}
+    dev: false
+
   /picocolors@1.1.1:
     resolution: {integrity: sha512-xceH2snhtb5M9liqDsmEw56le376mTZkEX/jEb/RxNFyegNul7eNslCXP9FDj/Lcu0X8KEyMceP2ntpaHrDEVA==}