fix: validate blocknote JSON in rich text fields (#18902)

## Summary
- **Backend**: Add JSON validation for the `blocknote` subfield in rich
text API inputs — rejects values that aren't valid JSON or aren't arrays
(BlockNote content is always `PartialBlock[]`). This prevents corrupted
data from being persisted to the database.
- **Frontend**: Replace all 5 unprotected `JSON.parse` calls on
blocknote content with the safe `parseJson` utility from
`twenty-shared`. Invalid content now degrades gracefully (empty block /
empty string / unchanged passthrough) instead of crashing the app.
- **Tests**: Added integration tests for invalid blocknote JSON (both
GraphQL and REST), unit tests for the new validation, and updated
existing test constants to use valid BlockNote JSON.

## Context
A user reported a `SyntaxError: Expected ',' or ']' after array element`
crash caused by malformed blocknote JSON stored in the database. The
data had `"children":[]` nested inside the `content` array instead of as
a sibling property. The API accepted this invalid JSON because it only
validated that `blocknote` was a string, not that it contained valid
JSON. On the frontend, 5 call sites used bare `JSON.parse` with no error
handling, causing a white-screen crash.

## Test plan
- [x] Unit tests pass: `validate-rich-text-field-or-throw.util.spec.ts`
(10/10)
- [x] Integration tests pass: `rich-text-field-create-input-validation`
(8/8)
- [ ] Verify creating a note with valid rich text still works end-to-end
- [ ] Verify API returns clear error when blocknote contains invalid
JSON
- [ ] Verify frontend renders empty block instead of crashing when
encountering corrupted data

🤖 Generated with [Claude Code](https://claude.com/claude-code)

packages/twenty-server/test/integration/graphql/suites/inputs-validation/create-validation/__snapshots__/rich-text-field-create-input-validation.integration-spec.ts.snap

@@ -2,4 +2,12 @@
 
 exports[`Create input validation - RICH_TEXT Gql create input - failure RICH_TEXT - should fail with : {"richTextField":"not-a-rich-text"} 1`] = `"Expected type "RichTextCreateInput" to be an object."`;
 
-exports[`Create input validation - RICH_TEXT Rest create input - failure RICH_TEXT - should fail with : {"richTextField":"not-a-rich-text"} 1`] = `"["Invalid rich text v2 value 'not-a-rich-text' for field \\"richTextField\\" - Should be an object"]"`;
+exports[`Create input validation - RICH_TEXT Gql create input - failure RICH_TEXT - should fail with : {"richTextField":{"blocknote":"[{\\"id\\":\\"1\\",\\"type\\":\\"paragraph\\",\\"props\\":{},\\"content\\":[{\\"type\\":\\"text\\",\\"text\\":\\"test\\"},\\"children\\":[]}]"}} 1`] = `"Invalid blocknote value for field "richTextField.blocknote" - must contain valid JSON"`;
+
+exports[`Create input validation - RICH_TEXT Gql create input - failure RICH_TEXT - should fail with : {"richTextField":{"blocknote":"invalid-json"}} 1`] = `"Invalid blocknote value for field "richTextField.blocknote" - must contain valid JSON"`;
+
+exports[`Create input validation - RICH_TEXT Rest create input - failure RICH_TEXT - should fail with : {"richTextField":"not-a-rich-text"} 1`] = `"["Invalid object value 'not-a-rich-text' for field \\"richTextField\\""]"`;
+
+exports[`Create input validation - RICH_TEXT Rest create input - failure RICH_TEXT - should fail with : {"richTextField":{"blocknote":"[{\\"id\\":\\"1\\",\\"type\\":\\"paragraph\\",\\"props\\":{},\\"content\\":[{\\"type\\":\\"text\\",\\"text\\":\\"test\\"},\\"children\\":[]}]"}} 1`] = `"["Invalid blocknote value for field \\"richTextField.blocknote\\" - must contain valid JSON"]"`;
+
+exports[`Create input validation - RICH_TEXT Rest create input - failure RICH_TEXT - should fail with : {"richTextField":{"blocknote":"invalid-json"}} 1`] = `"["Invalid blocknote value for field \\"richTextField.blocknote\\" - must contain valid JSON"]"`;

packages/twenty-server/test/integration/graphql/suites/inputs-validation/create-validation/constants/failing-create-input-by-field-metadata-type.constant.ts

@@ -230,6 +230,21 @@ export const failingCreateInputByFieldMetadataType: {
         richTextField: 'not-a-rich-text',
       },
     },
+    {
+      input: {
+        richTextField: {
+          blocknote: 'invalid-json',
+        },
+      },
+    },
+    {
+      input: {
+        richTextField: {
+          blocknote:
+            '[{"id":"1","type":"paragraph","props":{},"content":[{"type":"text","text":"test"},"children":[]}]',
+        },
+      },
+    },
   ],
   [FieldMetadataType.POSITION]: [
     {

packages/twenty-server/test/integration/graphql/suites/inputs-validation/create-validation/constants/successful-create-input-by-field-metadata-type.constant.ts

@@ -373,13 +373,15 @@ export const successfulCreateInputByFieldMetadataType: {
     {
       input: {
         richTextField: {
-          blocknote: 'test',
+          blocknote:
+            '[{"type":"paragraph","content":[{"type":"text","text":"test"}]}]',
           markdown: 'test',
         },
       },
       validateInput: (record: Record<string, any>) => {
         return (
-          record.richTextField.blocknote === 'test' &&
+          record.richTextField.blocknote ===
+            '[{"type":"paragraph","content":[{"type":"text","text":"test"}]}]' &&
           record.richTextField.markdown === 'test'
         );
       },