refactor(db): drop cleartext site/username column refs (columns removed)

User dropped the now-empty cleartext `site` + `username` columns after the
§1.3 migration completed. Removed every reference so the code matches the
schema: GET emission, POST/PUT/bulk INSERT/UPDATE (columns + params + binds).
title/tags cleartext columns still exist and are untouched.

decryptEntryMeta defaults e[f]='' for rows without *_enc (notes w/o site),
since GET no longer returns the dropped columns.

ponytail: contract phase of expand→migrate→contract; only safe because the
migration is proven complete (0 cleartext, both accounts).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

js/app.js

@@ -1482,6 +1482,8 @@ async function decryptEntryMeta(list) {
             if (enc && iv) {
                 const v = await decryptPwd(enc, iv);
                 if (v !== '[ERROR]') e[f] = v;
+            } else if (e[f] == null) {
+                e[f] = '';   // site/username cleartext columns dropped → default
             }
         }
     }