fix(confirmation): flag code-based OTP signups with no clickable link

Detect verification-code signups (e.g. "your verification code is
371404") whose only link is a mailto. These cleared the keyword
threshold but were dropped because the detector required an http(s)
candidate link. A code path now raises the flag/badge/banner when a
verification keyword sits next to an OTP-style code; the code is never
extracted or surfaced.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/application/email-processor.ts

@@ -236,7 +236,9 @@ async function storeEmail(
     ...(inlineIds.length > 0 ? { inlineAttachmentIds: inlineIds } : {}),
     ...(messageId ? { messageId } : {}),
     dedupHash,
-    ...(confirmationLinks
+    // null = not a confirmation; [] = a code-based confirmation (flag it, no
+    // link to surface). Both an empty and a populated array mean "detected".
+    ...(confirmationLinks !== null
       ? { confirmation: { links: confirmationLinks } }
       : {}),
   };