feat: add PDF and text file upload support (#205)

- Add client-side PDF text extraction using unpdf library
- Support text files (.txt, .md, .json, .csv, .py, .js, .ts, etc.)
- Add file preview with character count for PDF/text files
- Add 150k character limit for extracted content
- Highlight Paper to Diagram example with NEW badge
- Fix React hydration error by adding explicit IDs to ResizablePanelGroup
- Remove code duplication by centralizing file utilities in pdf-utils.ts

package-lock.json

@@ -54,6 +54,7 @@
                 "sonner": "^2.0.7",
                 "tailwind-merge": "^3.0.2",
                 "tailwindcss-animate": "^1.0.7",
+                "unpdf": "^1.4.0",
                 "zod": "^4.1.12"
             },
             "devDependencies": {
@@ -12514,6 +12515,20 @@
                 "url": "https://opencollective.com/unified"
             }
         },
+        "node_modules/unpdf": {
+            "version": "1.4.0",
+            "resolved": "https://registry.npmjs.org/unpdf/-/unpdf-1.4.0.tgz",
+            "integrity": "sha512-TahIk0xdH/4jh/MxfclzU79g40OyxtP00VnEUZdEkJoYtXAHWLiir6t3FC6z3vDqQTzc2ZHcla6uEiVTNjejuA==",
+            "license": "MIT",
+            "peerDependencies": {
+                "@napi-rs/canvas": "^0.1.69"
+            },
+            "peerDependenciesMeta": {
+                "@napi-rs/canvas": {
+                    "optional": true
+                }
+            }
+        },
         "node_modules/unrs-resolver": {
             "version": "1.11.1",
             "resolved": "https://registry.npmjs.org/unrs-resolver/-/unrs-resolver-1.11.1.tgz",