fix(e2e): match note-card locator on exact title, not substring content

noteCard() filtered on hasText, matching against a card's *entire*
rendered text — with note-linking, a card's content preview can now
render a linked note's title as plain text (a stripped note-link), so
a substring match against the whole card ambiguously resolves to more
than one card whenever one note's title happens to appear inside
another's preview. Scoped the match to the card's <h3> title element
with an anchored exact-match regex instead.

This was failing CI on two tests: the note-linking suite's own
backlink scenario, and — since test note titles aren't otherwise
isolated across files in the same run — an unrelated notes-crud test
whose note title happened to collide with a leftover "Linker Note"
card's rendered preview.

Verified: full e2e suite (114/114) passes locally against this fix.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/e2e/helpers/fixtures.ts

@@ -13,9 +13,18 @@ const COLLAB_EMAIL = 'collab@test.com';
 const COLLAB_PASSWORD = collabPassword;
 const COLLAB_NAME = 'Collaborator User';
 
-/** Find a specific note card by its title text */
+/**
+ * Find a specific note card by its exact title text. Matches only the
+ * card's <h3> title, not its full text content — with note-linking, a
+ * card's content preview can render another note's title as plain text
+ * (e.g. a stripped note-link), so a substring match against the whole
+ * card can ambiguously resolve to more than one card.
+ */
 export function noteCard(page: Page, title: string): Locator {
-	return page.locator('[data-testid="note-card"]', { hasText: title });
+	const escaped = title.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
+	return page.locator('[data-testid="note-card"]').filter({
+		has: page.locator('h3', { hasText: new RegExp(`^${escaped}$`) })
+	});
 }
 
 /**