feat(#3): Add PDF caching

CLAUDE.md

@@ -134,7 +134,7 @@ Forms can be exported as:
 
 Endpoints:
 - `GET /application-forms/{id}/html` - Returns HTML representation
-- `GET /application-forms/{id}/pdf` - Returns PDF (inline display)
+- `GET /application-forms/{id}/versions/{versionNumber}/pdf` - Returns version PDF (inline display)
 
 ### 6. Comments System
 
@@ -585,7 +585,7 @@ Migrations are managed manually using **Liquibase** in `src/main/resources/db/ch
 - `GET /application-forms/{id}` - Get form by ID
 - `PUT /application-forms/{id}` - Update form
 - `DELETE /application-forms/{id}` - Delete form
-- `GET /application-forms/{id}/pdf` - Export as PDF
+- `GET /application-forms/{id}/versions/{versionNumber}/pdf` - Export a version as PDF
 - `GET /application-forms/{id}/html` - Export as HTML
 - `POST /application-forms/{id}/submit` - Submit form
 - `POST /application-forms/{applicationFormId}/subsections/{subsectionId}/form-elements?position={n}` - Add form element dynamically
@@ -741,7 +741,7 @@ act -n
    - Any change that touches form element types, options/value storage, visibility conditions, or section spawning can break PDF output.
    - Always validate **both** HTML and PDF export for a real form instance (including newly spawned sections and newly added text fields with values):
      - `GET /application-forms/{id}/html`
-     - `GET /application-forms/{id}/pdf`
+     - `GET /application-forms/{id}/versions/{versionNumber}/pdf`
    - Verify these render correctly (with saved values):
      - `TEXTFIELD`, `TEXTAREA`, `DATE`, `RICH_TEXT`
      - `SELECT`, `RADIOBUTTON`, `CHECKBOX`, `SWITCH`