Fix data-URI screenshots not opening on click (Chrome blocks data: URL navigation)

The click-to-zoom feature from the previous commit worked for cid:-referenced
images but silently failed for images embedded directly as a data: URI —
confirmed with a real Playwright click: Chrome refuses to navigate a tab
(even a new one, even from a direct user click) to a data: URL, so
<a href="data:...' target="_blank"> just does nothing. The cursor still
showed zoom-in on hover since that's plain CSS, which is exactly the "лупа
появляется, но не нажимается" symptom reported.

Fix: imap.ts now extracts every data:image src out of an inbound email's
HTML into a real attachment file (deduping identical images embedded more
than once), the same way cid: images already were, and rewrites the HTML to
point at that attachment's normal /api/attachments/... URL instead. That
also shrinks messages.body_html (data URIs can be hundreds of KB sitting in
a DB column) and gets data-URI images the same "no duplicate chip below"
treatment cid: images already had.

attachments.isInline is now its own real column (backfilled from the
existing content_id-based cases) instead of being derived from content_id,
since a data-URI-derived attachment is inline but was never cid-referenced.
sanitizeEmailHtml's link-wrapping step now skips any residual data: src
defensively (unwrapped-but-visible beats a link that looks clickable but
isn't).

Verified against the real deployment with actual browser clicks (Playwright):
both a data-URI image and a cid: image now open their full-resolution
attachment in a new tab; before this fix the data-URI one silently did
nothing. Added a vitest.config.ts (needed for the new test file's @/ import
aliases) and unit tests for the extraction/dedup logic.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GteWhnWKTmnXcsd5jx6H7u

vitest.config.ts

@@ -0,0 +1,10 @@
+import { defineConfig } from "vitest/config";
+import path from "node:path";
+
+export default defineConfig({
+  resolve: {
+    alias: {
+      "@": path.resolve(__dirname, "./src"),
+    },
+  },
+});