Add live dashboard with SSE job events

Expose /jobs, /dedup, and /events routes backed by a new EventBus that
broadcasts job lifecycle and per-job progress over SSE. Serve a static
dashboard from front/ that lists pending and in-progress jobs, streams
agent activity, and shows completed reviews.

Also add migrate-apply/migrate-generate scripts that load .env, update
the Containerfile to ship the front assets and use the apply script, and
refresh the roadmap.

front/js/theme-toggle.js

@@ -0,0 +1,59 @@
+// Bascule de thème, identique à celle du site public (même clé localStorage,
+// même rendu), empaquetée en web component.
+
+const STORAGE_KEY = "steep-theme";
+
+export function currentTheme() {
+  return document.documentElement.dataset.theme === "light" ? "light" : "dark";
+}
+
+export function applyTheme(theme, persist = true) {
+  document.documentElement.dataset.theme = theme;
+
+  const meta = document.querySelector('meta[name="theme-color"]');
+  if (meta) meta.content = theme === "dark" ? "#0b1520" : "#f7f8f5";
+
+  if (persist) {
+    try {
+      localStorage.setItem(STORAGE_KEY, theme);
+    } catch (_) {
+      // stockage indisponible : on garde juste le thème en mémoire.
+    }
+  }
+
+  window.dispatchEvent(new CustomEvent("steep:theme", { detail: theme }));
+}
+
+class ThemeToggle extends HTMLElement {
+  connectedCallback() {
+    this.innerHTML = `
+      <button class="theme-toggle" type="button" role="switch" aria-label="Toggle color theme">
+        <span class="theme-icon" aria-hidden="true"></span><span class="theme-label"></span>
+      </button>`;
+
+    this._button = this.querySelector("button");
+    this._icon = this.querySelector(".theme-icon");
+    this._label = this.querySelector(".theme-label");
+    this._onTheme = () => this.render();
+
+    this._button.addEventListener("click", () => {
+      applyTheme(currentTheme() === "dark" ? "light" : "dark");
+    });
+    window.addEventListener("steep:theme", this._onTheme);
+
+    this.render();
+  }
+
+  disconnectedCallback() {
+    window.removeEventListener("steep:theme", this._onTheme);
+  }
+
+  render() {
+    const theme = currentTheme();
+    this._icon.textContent = theme === "dark" ? "☾" : "☀";
+    this._label.textContent = theme === "dark" ? "Dark theme" : "Light theme";
+    this._button.setAttribute("aria-checked", String(theme === "dark"));
+  }
+}
+
+customElements.define("steep-theme-toggle", ThemeToggle);