feat(attachments): render inline cid images in place, not as attachments

Inline images (referenced by src="cid:…") are now classified at ingest and
kept out of the downloadable attachment lists, RSS/Atom enclosures, and the
API — while still stored in R2 and cleaned up with the email. Fixes the admin
email preview, which injected raw HTML into the data: iframe so cid refs never
resolved; it now rewrites them to absolute /files URLs.

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

src/routes/api/index.ts

@@ -325,13 +325,15 @@ apiApp.openapi(
         from: data.from,
         receivedAt: data.receivedAt,
         content: data.content,
-        attachments: (data.attachments ?? []).map((a) => ({
-          id: a.id,
-          filename: a.filename,
-          contentType: a.contentType,
-          size: a.size,
-          url: `/files/${a.id}/${encodeURIComponent(a.filename)}`,
-        })),
+        attachments: (data.attachments ?? [])
+          .filter((a) => !a.inline)
+          .map((a) => ({
+            id: a.id,
+            filename: a.filename,
+            contentType: a.contentType,
+            size: a.size,
+            url: `/files/${a.id}/${encodeURIComponent(a.filename)}`,
+          })),
       },
       200,
     );