feat: browser UI – unlock, table view, create/edit/delete with client-side crypto

Vanilla HTML/CSS/JS frontend served by Flask:
- Unlock screen: passphrase -> Argon2id session key, held in memory
  only (never sent to the server); "Sperren" wipes key and DOM rows.
- Records table (Person A/B, start/end, action) rendered via
  textContent only (no HTML injection); undecryptable rows are flagged.
- Create/edit modal encrypts payloads with XChaCha20-Poly1305 before
  any network call; updates carry the server version (optimistic lock,
  conflict toast on 409); delete fetches current version first.

🤖 Generated with Codebuff
Co-Authored-By: Codebuff <noreply@codebuff.com>

backend/static/style.css

@@ -0,0 +1,129 @@
+/* crushdb – simple, clean dark UI */
+
+:root {
+  --bg: #101418;
+  --panel: #1a2028;
+  --panel-2: #202830;
+  --border: #2c3642;
+  --text: #e6edf3;
+  --muted: #8b98a5;
+  --accent: #4da3ff;
+  --danger: #ff5d5d;
+  --ok: #47d68a;
+}
+
+* { box-sizing: border-box; }
+
+body {
+  margin: 0 auto;
+  max-width: 960px;
+  padding: 2rem 1rem;
+  font-family: system-ui, -apple-system, "Segoe UI", sans-serif;
+  background: var(--bg);
+  color: var(--text);
+  line-height: 1.5;
+}
+
+h1 { margin: 0 0 0.25rem; font-size: 1.6rem; }
+.tagline { margin: 0 0 1.5rem; color: var(--muted); }
+
+#flash {
+  min-height: 1.4rem;
+  margin-bottom: 1rem;
+  color: var(--ok);
+}
+#flash.error { color: var(--danger); }
+
+#unlock {
+  max-width: 420px;
+  margin: 3rem auto;
+  background: var(--panel);
+  border: 1px solid var(--border);
+  border-radius: 10px;
+  padding: 1.5rem;
+}
+
+#unlock label { display: block; margin-bottom: 0.5rem; }
+#unlock input {
+  width: 100%;
+  margin-bottom: 1rem;
+}
+.hint { color: var(--muted); font-size: 0.85rem; margin-top: 1rem; }
+
+input, button {
+  font: inherit;
+  color: var(--text);
+}
+
+input {
+  background: var(--panel-2);
+  border: 1px solid var(--border);
+  border-radius: 6px;
+  padding: 0.5rem 0.7rem;
+}
+input:focus { outline: 1px solid var(--accent); }
+
+button {
+  background: var(--accent);
+  color: #0b1016;
+  border: none;
+  border-radius: 6px;
+  padding: 0.5rem 1rem;
+  cursor: pointer;
+  font-weight: 600;
+}
+button:hover { filter: brightness(1.1); }
+
+#app .toolbar {
+  display: flex;
+  gap: 0.75rem;
+  margin-bottom: 1rem;
+}
+#lock-btn { background: var(--panel-2); color: var(--text); border: 1px solid var(--border); }
+
+table {
+  width: 100%;
+  border-collapse: collapse;
+  background: var(--panel);
+  border: 1px solid var(--border);
+  border-radius: 10px;
+  overflow: hidden;
+}
+
+th, td {
+  padding: 0.6rem 0.75rem;
+  text-align: left;
+  border-bottom: 1px solid var(--border);
+}
+thead th { background: var(--panel-2); color: var(--muted); font-weight: 600; }
+tbody tr:last-child td { border-bottom: none; }
+tbody tr:hover { background: var(--panel-2); }
+
+.row-error td { color: var(--danger); font-size: 0.9rem; }
+
+td:last-child, td button { white-space: nowrap; }
+td button + button { margin-left: 0.4rem; }
+
+/* modal */
+#editor-backdrop {
+  position: fixed;
+  inset: 0;
+  background: rgba(0, 0, 0, 0.6);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}
+
+#editor {
+  background: var(--panel);
+  border: 1px solid var(--border);
+  border-radius: 10px;
+  padding: 1.5rem;
+  width: min(440px, 92vw);
+}
+
+#editor h2 { margin-top: 0; font-size: 1.15rem; }
+#editor label { display: block; margin-bottom: 0.75rem; color: var(--muted); }
+#editor input { width: 100%; margin-top: 0.25rem; }
+#editor .actions { display: flex; gap: 0.75rem; margin-top: 1rem; }
+#editor-cancel { background: var(--panel-2); color: var(--text); border: 1px solid var(--border); }