feat: FEAT-05 — DTC history sync to remote server

- Server: dtc_events table (migrate_phase27_dtc.sql), db.py helpers
  (upsert_dtc_snapshot, list_dtc_events, delete_dtc_event)
- Server API: POST /api/v1/dtc/batch (device auth), GET/DELETE /api/v1/portal/dtc
- Server portal: /dtc page with code, description, MIL, status, timestamps, delete
- Server nav: DTC history in sidebar + mobile bottom nav
- Pi: _upload_dtc_snapshot() in app_upload.py — uploads when snapshot changes,
  skips when OBD disconnected or unchanged

server/templates/base.html

@@ -49,6 +49,11 @@
                     <i class="fas fa-video fa-fw"></i><span>Dashcam archive</span>
                 </a>
             </li>
+            <li class="nav-item">
+                <a class="nav-link{% if request.endpoint == 'portal_dtc_page' %} active{% endif %}" href="{{ url_for('portal_dtc_page') }}">
+                    <i class="fas fa-exclamation-triangle fa-fw"></i><span>DTC history</span>
+                </a>
+            </li>
             <li class="nav-item">
                 <a class="nav-link{% if request.endpoint == 'portal_device_settings_page' %} active{% endif %}" href="{{ url_for('portal_device_settings_page') }}">
                     <i class="fas fa-sliders-h fa-fw"></i><span>Device settings</span>
@@ -117,6 +122,10 @@
             <i class="fas fa-sliders-h"></i>
             <span>Device</span>
         </a>
+        <a class="mobile-nav-item{% if request.endpoint == 'portal_dtc_page' %} active{% endif %}" href="{{ url_for('portal_dtc_page') }}">
+            <i class="fas fa-exclamation-triangle"></i>
+            <span>DTC</span>
+        </a>
         <a class="mobile-nav-item" href="{{ url_for('logout') }}">
             <i class="fas fa-sign-out-alt"></i>
             <span>Logout</span>

server/templates/dtc.html

@@ -0,0 +1,94 @@
+{% extends "base.html" %}
+
+{% block title %}DTC history – Yaris OBD Remote{% endblock %}
+
+{% block content %}
+<h3 class="text-dark mb-3 fw-bold">DTC history</h3>
+
+<div class="row g-3">
+    <div class="col-12">
+        <div class="card shadow-sm">
+            <div class="card-header py-2 d-flex justify-content-between align-items-center">
+                <h6 class="text-primary fw-bold m-0">Diagnostic trouble codes</h6>
+                <span id="dtc-count" class="badge bg-secondary">0</span>
+            </div>
+            <div class="card-body p-0">
+                <div id="dtc-loading" class="text-center text-muted py-4">
+                    <span class="spinner-border spinner-border-sm me-2" aria-hidden="true"></span>
+                    Loading…
+                </div>
+                <div id="dtc-error" class="alert alert-danger m-3" role="alert" hidden></div>
+                <div class="table-responsive">
+                    <table class="table table-sm table-hover mb-0" id="dtc-table" hidden>
+                        <thead class="table-light">
+                            <tr>
+                                <th class="ps-3">Code</th>
+                                <th>Description</th>
+                                <th>MIL</th>
+                                <th>Status</th>
+                                <th>First seen</th>
+                                <th>Last seen</th>
+                                <th class="pe-3">Actions</th>
+                            </tr>
+                        </thead>
+                        <tbody id="dtc-body"></tbody>
+                    </table>
+                </div>
+                <div id="dtc-empty" class="text-muted text-center py-4 small" hidden>No DTC events recorded yet.</div>
+            </div>
+        </div>
+    </div>
+</div>
+{% endblock %}
+
+{% block scripts %}
+<script>
+(function () {
+    const loading = document.getElementById("dtc-loading");
+    const error = document.getElementById("dtc-error");
+    const table = document.getElementById("dtc-table");
+    const tbody = document.getElementById("dtc-body");
+    const empty = document.getElementById("dtc-empty");
+    const count = document.getElementById("dtc-count");
+
+    function fmt(iso) { return iso ? new Date(iso).toLocaleString() : "—"; }
+
+    async function load() {
+        try {
+            const r = await fetch("/api/v1/portal/dtc");
+            if (!r.ok) throw new Error("Cannot load DTC events.");
+            const events = await r.json();
+            loading.hidden = true;
+            count.textContent = events.length;
+            if (!events.length) { empty.hidden = false; return; }
+            tbody.innerHTML = events.map(e => `
+                <tr>
+                    <td class="ps-3 fw-bold font-monospace ${e.is_active ? 'text-danger' : 'text-muted'}">${e.code}</td>
+                    <td>${e.description || "—"}</td>
+                    <td>${e.mil_on ? '<span class="badge text-bg-warning">ON</span>' : '<span class="badge text-bg-secondary">OFF</span>'}</td>
+                    <td>${e.is_active ? '<span class="badge text-bg-danger">Active</span>' : '<span class="badge text-bg-success">Cleared</span>'}</td>
+                    <td class="small text-muted">${fmt(e.first_seen_at)}</td>
+                    <td class="small text-muted">${fmt(e.last_seen_at)}</td>
+                    <td class="pe-3"><button class="btn btn-sm btn-outline-danger" data-dtc-id="${e.id}" title="Delete">🗑</button></td>
+                </tr>
+            `).join("");
+            table.hidden = false;
+
+            tbody.querySelectorAll("[data-dtc-id]").forEach(btn => {
+                btn.addEventListener("click", async () => {
+                    if (!confirm("Delete this DTC event?")) return;
+                    const r = await fetch("/api/v1/portal/dtc/" + btn.dataset.dtcId, {method: "DELETE"});
+                    if (!r.ok) { error.textContent = "Could not delete."; error.hidden = false; return; }
+                    load();
+                });
+            });
+        } catch (e) {
+            loading.hidden = true;
+            error.textContent = e.message;
+            error.hidden = false;
+        }
+    }
+    load();
+})();
+</script>
+{% endblock %}