feat: free-text timestamps instead of datetime pickers

Users wanted to type things like "unbekannt" or comments for the date
fields. Start/End are now plain text inputs (max 120 chars) and are
stored/displayed verbatim - no Date parsing, no formatting. Existing
records that contain ISO strings keep working: they render exactly as
stored and refill the edit form unchanged. Also removes a duplicated
block in setup() that had slipped in earlier (double reload/flash).

Verified: node --check, no datetime-local/Date-parsing remnants,
crypto roundtrip with free-text and legacy ISO timestamps, pytest 3/3.

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

backend/static/ui.js

@@ -91,10 +91,10 @@ async function api(path, opts = {}) {
 
 // ---------- rendering ----------
 
-function iso(ts) {
-  if (ts === null || ts === "") return "–";
-  const d = new Date(ts);
-  return isNaN(d) ? String(ts) : d.toLocaleString();
+// Timestamps are free text now ("unknown", "Sommer 2025", …). Display
+// them verbatim; nothing to parse or format.
+function showTs(value) {
+  return (value === null || value === undefined || value === "") ? "–" : String(value);
 }
 
 function renderRow(record, payload) {
@@ -102,8 +102,8 @@ function renderRow(record, payload) {
   const cells = [
     payload.personA,
     payload.personB,
-    iso(payload.tsStart),
-    iso(payload.tsEnd),
+    showTs(payload.tsStart),
+    showTs(payload.tsEnd),
     payload.action,
   ];
   for (const text of cells) {
@@ -162,8 +162,8 @@ function openEditor(record, payload) {
   $("#editor-title").textContent = "Datensatz bearbeiten";
   $("#f-persona").value = payload.personA ?? "";
   $("#f-personb").value = payload.personB ?? "";
-  $("#f-tsstart").value = payload.tsStart ? new Date(payload.tsStart).toISOString().slice(0, 16) : "";
-  $("#f-tsend").value = payload.tsEnd ? new Date(payload.tsEnd).toISOString().slice(0, 16) : "";
+  $("#f-tsstart").value = payload.tsStart ?? "";
+  $("#f-tsend").value = payload.tsEnd ?? "";
   $("#f-action").value = payload.action ?? "";
   $("#editor-backdrop").hidden = false;
 }
@@ -184,9 +184,9 @@ function closeEditor() {
 }
 
 function tsOrNull(inputValue) {
-  if (!inputValue) return null;
-  const d = new Date(inputValue);
-  return isNaN(d) ? null : d.toISOString();
+  // Free-text field: trim to null or the plain string.
+  const v = inputValue.trim();
+  return v === "" ? null : v;
 }
 
 // ---------- record operations ----------
@@ -275,10 +275,6 @@ async function setup(ev) {
       resetSession();
       return;
     }
-    $("#passphrase").value = "";
-    $("#setup").hidden = true;
-    $("#app").hidden = false;
-    await reload();
     $("#setup-pass1").value = "";
     $("#setup-pass2").value = "";
     $("#setup").hidden = true;