feat(editor): add permanent global toggle for code block line numbers (#15381)

Add a persistent "Show line numbers in code blocks" setting to Editor
Settings that controls line-number visibility across all code blocks.
Individual blocks can still override the global default via the
per-block More menu toggle.

## Changes

- **schema.ts** - add `codeBlockLineNumbers: z.boolean().default(true)`
to `AffineEditorSettingSchema`
- **code-block.ts** - read `codeBlockLineNumbers` from
`EditorSettingProvider` reactively via a stable `signal(true)` updated
by `effect()` in `connectedCallback`; expose `showLineNumbers` getter as
single source of truth used by both `renderBlock()` and the toolbar
- **config.ts** - toolbar line-number toggle reads
`blockComponent.showLineNumbers` (resolved state) instead of
`model.props.lineNumber ?? true`
- **general.tsx** - add `DefaultCodeBlockLineNumberSettings` Switch row
in editor general settings
- **en.json + i18n.gen.ts** - add i18n strings for the new setting
- **line-numbers.spec.ts** - add 7 e2e tests covering default
visibility, global toggle on/off, per-block override in both directions,
multi-block, newly created blocks, and persistence across reload

## Behaviour

| State | Result |
|---|---|
| Global ON (default), no per-block override | Line numbers shown |
| Global OFF, no per-block override | Line numbers hidden |
| Global OFF, per-block explicitly ON | Line numbers shown |
| Global ON, per-block explicitly OFF | Line numbers hidden |
| Mobile (feature flag) | Always hidden regardless of settings |

## Notes

- Existing per-block toggle behaviour is fully preserved and unchanged
- Default is `true` so no regression for existing users
- The blocksuite-side reads `codeBlockLineNumbers` via a type cast (`as
Record<string, unknown>`) because the key lives in the AFFiNE-level
`EditorSettingSchema`, not in blocksuite's own `GeneralSettingSchema` -
this is an intentional architectural boundary

Closes #14965


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added a global setting to show or hide line numbers in code blocks by
default.
  * Added localized title and description text for the new setting.
  * Preserved per-code-block overrides through the block’s More menu.

* **Bug Fixes**
* Line-number visibility now stays consistent across existing and newly
created code blocks, including after reloads.

* **Tests**
* Added end-to-end coverage for defaults, overrides, persistence, and
multiple code blocks.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/i18n/src/i18n.gen.ts

@@ -5497,6 +5497,14 @@ export function useAFFiNEI18N(): {
       * `Code blocks default language`
       */
     ["com.affine.settings.editorSettings.general.default-code-block.language.title"](): string;
+    /**
+      * `Show line numbers in all code blocks by default.`
+      */
+    ["com.affine.settings.editorSettings.general.default-code-block.line-numbers.description"](): string;
+    /**
+      * `Show line numbers in code blocks`
+      */
+    ["com.affine.settings.editorSettings.general.default-code-block.line-numbers.title"](): string;
     /**
       * `Encapsulate code snippets for better readability.`
       */

packages/frontend/i18n/src/resources/en.json

@@ -1368,6 +1368,8 @@
   "com.affine.settings.editorSettings.general.ai.title": "AFFiNE AI",
   "com.affine.settings.editorSettings.general.default-code-block.language.description": "Set a default programming language.",
   "com.affine.settings.editorSettings.general.default-code-block.language.title": "Code blocks default language",
+  "com.affine.settings.editorSettings.general.default-code-block.line-numbers.description": "Show line numbers in all code blocks by default.",
+  "com.affine.settings.editorSettings.general.default-code-block.line-numbers.title": "Show line numbers in code blocks",
   "com.affine.settings.editorSettings.general.default-code-block.wrap.description": "Encapsulate code snippets for better readability.",
   "com.affine.settings.editorSettings.general.default-code-block.wrap.title": "Wrap code in code blocks",
   "com.affine.settings.editorSettings.general.default-new-doc.description": "Default mode for new doc.",