test: tag two line-numbers-touching pad_settings specs with @feature:line-numbers (#7658)

Surfaced by ep_hide_line_numbers' red main. Two pad_settings specs
use `expect(...).not.toHaveClass(/line-numbers-hidden/)` to verify
the line-number gutter is visible by default before settings flip
it on, but plugins that hide line numbers (ep_hide_line_numbers
sets `pad.changeViewOption('showLineNumbers', false)` in postAceInit)
keep that class on the body for the entire pad lifetime.

Tag the two affected specs with @feature:line-numbers so plugins
that hide line numbers can declare `disables: ["@feature:line-numbers"]`
in ep.json and have these excluded from pass-1 regression while
still failing pass-2 honesty (plugin must actually keep them hidden).

Companion to the existing tag set (@feature:chat, @feature:username,
@feature:clear-authorship, @feature:error-gritter,
@feature:authorship-bg-color). See doc/PLUGIN_FEATURE_DISABLES.md.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: JohnMcLear

src/tests/frontend-new/specs/pad_settings.spec.ts

@@ -28,7 +28,9 @@ test.describe('creator-owned pad settings', () => {
     await context2.close();
   });
 
-  test('pad settings act as defaults until enforcement is enabled', async ({page, browser}) => {
+  test('pad settings act as defaults until enforcement is enabled', {
+    tag: '@feature:line-numbers',
+  }, async ({page, browser}) => {
     const padId = await goToNewPad(page);
 
     const context2 = await browser.newContext();
@@ -122,7 +124,9 @@ test.describe('creator-owned pad settings', () => {
         await context2.close();
       });
 
-  test('uses My View defaults for newly created pads without changing an existing pad default',
+  test('uses My View defaults for newly created pads without changing an existing pad default', {
+    tag: '@feature:line-numbers',
+  },
       async ({page}) => {
         await goToNewPad(page);
         const creatorOuter = page.frameLocator('iframe[name="ace_outer"]').locator('#outerdocbody');