feat(auth): login, roles, user mgmt, setup wizard, and session guard

- New skald-setup crate: interactive first-run wizard that creates the
  admin user, prompts for encryption choice and password
- Auth system: session-based login/logout with cookie, guard middleware
- Roles API: CRUD for data-driven roles, seeded on first boot
- Users management API: create, list, edit, delete users
- Setup state API: check if first admin has been created
- Frontend: login-page, setup-page, users-page, roles-page, profile-page
  components with corresponding CSS
- Topbar: avatar dropdown with profile link and logout
- Sidebar: nav entries for Users and Roles (admin only)
- Page shell CSS: layout support for the new pages
- build.sh: builds both skald and skald-setup binaries
- run.sh: runs skald-setup before the server loop
- CLAUDE.md: updated workspace layout and build/run docs

web/css/setup-page.css

@@ -0,0 +1,107 @@
+.setup-page,
+.login-page {
+  position: fixed;
+  inset: 0;
+  z-index: 9999;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  background: var(--bs-body-bg);
+  overflow: auto;
+  padding: 24px;
+}
+
+.setup-card,
+.login-card {
+  width: 100%;
+  max-width: 440px;
+  background: var(--card-bg);
+  border: 1px solid var(--card-border);
+  border-radius: 8px;
+  box-shadow: var(--card-shadow);
+  padding: 36px 32px;
+}
+
+.setup-logo,
+.login-logo {
+  text-align: center;
+  margin-bottom: 24px;
+}
+
+.setup-logo img,
+.login-logo img {
+  width: 64px;
+  height: 64px;
+  border-radius: 14px;
+}
+
+.setup-title,
+.login-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  text-align: center;
+  margin: 0 0 6px;
+}
+
+.setup-subtitle,
+.login-subtitle {
+  text-align: center;
+  color: var(--placeholder-color);
+  font-size: .9rem;
+  margin: 0 0 28px;
+}
+
+.setup-error,
+.login-error {
+  background: rgba(220, 53, 69, .1);
+  border: 1px solid rgba(220, 53, 69, .35);
+  border-radius: var(--card-radius);
+  padding: 10px 14px;
+  margin-bottom: 18px;
+  font-size: .85rem;
+  color: #dc3545;
+}
+
+.setup-warn {
+  background: rgba(255, 193, 7, .1);
+  border: 1px solid rgba(255, 193, 7, .35);
+  border-radius: var(--card-radius);
+  padding: 12px 14px;
+  margin-top: 18px;
+  font-size: .82rem;
+  color: var(--bs-secondary-color);
+}
+
+.setup-warn strong {
+  color: #b8860b;
+}
+
+[data-bs-theme="dark"] .setup-warn strong {
+  color: #ffc107;
+}
+
+.setup-submit,
+.login-submit {
+  width: 100%;
+  margin-top: 24px;
+}
+
+.setup-spinner,
+.login-spinner {
+  width: 16px;
+  height: 16px;
+  border: 2px solid currentColor;
+  border-right-color: transparent;
+  border-radius: 50%;
+  display: inline-block;
+  animation: setup-spin .65s linear infinite;
+  vertical-align: -3px;
+  margin-right: 6px;
+}
+
+@keyframes setup-spin {
+  to { transform: rotate(360deg); }
+}
+.login-spinner {
+  animation-name: setup-spin;
+}