Add PDF translation API, utilities, docs, and config

Introduces core backend and frontend infrastructure for a PDF translation interface. Adds API endpoints for translation, PDF testing, and AI provider testing; implements PDF text extraction, cost tracking, and pricing logic in the lib directory; adds reusable UI components; and provides comprehensive documentation (SDD, environment setup, Claude instructions). Updates Tailwind and global styles, and includes a sample test PDF and configuration files.

.claude/settings.local.json

@@ -0,0 +1,18 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(npm install:*)",
+      "Bash(npm run build:*)",
+      "Bash(npm run dev:*)",
+      "Bash(npm ls:*)",
+      "Bash(node:*)",
+      "Bash(npm uninstall:*)",
+      "Bash(curl:*)",
+      "Bash(taskkill:*)",
+      "Bash(powershell:*)",
+      "Bash(npx next dev:*)",
+      "Bash(rm:*)"
+    ],
+    "defaultMode": "acceptEdits"
+  }
+}