Implement left/right voting on entries

GET /entry/{pid}/interactions/{mode} now reads the vote tally and, for
mode=left/right (auth required), toggles the user's vote: new vote, repeat
same mode removes it, different mode switches. Returns {left, right,
selected}. A UNIQUE(uid, pid) constraint on the vote table prevents
duplicate votes. The JS frontend renders Links/Rechts buttons with live
counts under each entry.

This completes the voting feature that was left commented-out and broken
in the Flask version.

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

web/css/app.css

@@ -73,3 +73,23 @@ button:hover { opacity: 0.9; }
 
 .msg { color: #ff6b6b; font-size: 0.9rem; min-height: 1.2em; }
 .end { text-align: center; color: var(--muted); padding: 2rem 0; }
+
+.interactions {
+  display: flex;
+  align-items: center;
+  gap: 0.75rem;
+  margin-top: 0.8rem;
+}
+.interactions .vote {
+  background: transparent;
+  border: 1px solid #2a2e35;
+  color: var(--fg);
+  padding: 0.3rem 0.7rem;
+}
+.interactions .vote:hover { border-color: var(--accent); }
+.interactions .vote.selected {
+  background: var(--accent);
+  border-color: var(--accent);
+  color: #fff;
+}
+.interactions .counts { color: var(--muted); font-size: 0.9rem; }