fix(import): consistent add-source forms with masked passwords and URL errors

- Mask the Xtream password in add and edit (and the Stalker one in edit)
  behind a shared PasswordVisibilityToggleDirective: one translated
  "Show password" label, state in aria-pressed, type="button".
- Give the Xtream server URL its own mat-error and a neutral hint instead
  of the EPG file error; give the M3U URL a mat-error.
- Use "Playlist title" in every add form, "MAC address" casing, a single
  ellipsis in "Validating portal…" and one "Add playlist" submit label;
  translate the method radiogroup's aria-label.
- Show Stalker refusals inline under the portal URL (role="status", like
  the Xtream connection test), translated in the template and cleared by
  edits; translate the snackbars for outcomes that close the dialog.
- Translate new strings into all locales; reuse the identical Stalker URL
  error translations; fix MAC casing and ellipses; drop unused keys.
- Unit specs per form, edit-dialog spec, new add-source-forms web E2E;
  update E2E locators; UI guidelines Forms section; Stalker contract.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/electron-backend-e2e/src/dash-clearkey.e2e.ts

@@ -193,7 +193,9 @@ async function importDashPlaylistFromText(
     const dialog = app.mainWindow.locator('mat-dialog-container').last();
     await dialog.getByRole('radio', { name: /Raw m3u text/i }).click();
     await dialog.locator('textarea').fill(playlist);
-    await dialog.getByRole('button', { name: 'Import', exact: true }).click();
+    await dialog
+        .getByRole('button', { name: 'Add playlist', exact: true })
+        .click();
     await dialog.waitFor({ state: 'detached' });
     await waitForM3uCatalog(app.mainWindow);
 }

apps/electron-backend-e2e/src/sources.e2e.ts

@@ -91,7 +91,7 @@ test.describe('Electron Sources View', () => {
                 path: test.info().outputPath('http-connection-add.png'),
             });
             await dialog
-                .getByRole('button', { name: 'Add', exact: true })
+                .getByRole('button', { name: 'Add playlist', exact: true })
                 .click();
             await waitForXtreamCatalog(page);
             await openSources(page);

apps/electron-backend-e2e/src/xtream-live-format.fixture.ts

@@ -40,7 +40,9 @@ export async function addLiveFormatPortal(page: Page) {
     await dialog.locator('#serverUrl').fill(liveFormatMock);
     await dialog.locator('#username').fill('live-fallback');
     await dialog.locator('#password').fill('live-fallback');
-    await dialog.getByRole('button', { name: 'Add', exact: true }).click();
+    await dialog
+        .getByRole('button', { name: 'Add playlist', exact: true })
+        .click();
     await page.waitForURL(/xtreams.*vod/);
     await page.getByRole('link', { name: 'Live TV', exact: true }).click();
     await page.locator('.context-panel .category-item').first().click();