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

Cargo.lock

@@ -4345,7 +4345,7 @@ version = "0.13.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "be769465445e8c1474e9c5dac2018218498557af32d9ed057325ec9a41ae81bf"
 dependencies = [
- "heck 0.4.1",
+ "heck 0.5.0",
  "itertools 0.14.0",
  "log",
  "multimap",
@@ -4869,6 +4869,27 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "rpassword"
+version = "7.5.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2da316a15f47e3d053de9cb2c439650bd8fa4aaeb9365f2e5f27f492ff73c196"
+dependencies = [
+ "libc",
+ "rtoolbox",
+ "windows-sys 0.61.2",
+]
+
+[[package]]
+name = "rtoolbox"
+version = "0.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "50a0e551c1e27e1731aba276dbeaeac73f53c7cd34d1bda485d02bd1e0f36844"
+dependencies = [
+ "libc",
+ "windows-sys 0.59.0",
+]
+
 [[package]]
 name = "rustc-hash"
 version = "2.1.2"
@@ -5617,6 +5638,16 @@ dependencies = [
  "uuid",
 ]
 
+[[package]]
+name = "skald-setup"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "rpassword",
+ "skald-core",
+ "tokio",
+]
+
 [[package]]
 name = "slab"
 version = "0.4.12"
@@ -6467,7 +6498,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "32497e9a4c7b38532efcdebeef879707aa9f794296a4f0244f6f69e9bc8574bd"
 dependencies = [
  "fastrand",
- "getrandom 0.3.4",
+ "getrandom 0.4.2",
  "once_cell",
  "rustix",
  "windows-sys 0.61.2",