Add phx.gen.auth authentication scaffolding

- LiveView-based email/password auth via mix phx.gen.auth
- Auth links removed from public navigation (direct URL access only)
- Accounts context with User schema and token management

app/lib/firehose_web/controllers/user_settings_html/edit.html.heex

@@ -0,0 +1,47 @@
+<div class="text-center">
+  <.header>
+    Account Settings
+    <:subtitle>Manage your account email address and password settings</:subtitle>
+  </.header>
+</div>
+
+<.form :let={f} for={@email_changeset} action={~p"/users/settings"} id="update_email">
+  <input type="hidden" name="action" value="update_email" />
+
+  <.input
+    field={f[:email]}
+    type="email"
+    label="Email"
+    autocomplete="username"
+    spellcheck="false"
+    required
+  />
+
+  <.button variant="primary" phx-disable-with="Changing...">Change Email</.button>
+</.form>
+
+<div class="divider" />
+
+<.form :let={f} for={@password_changeset} action={~p"/users/settings"} id="update_password">
+  <input type="hidden" name="action" value="update_password" />
+
+  <.input
+    field={f[:password]}
+    type="password"
+    label="New password"
+    autocomplete="new-password"
+    spellcheck="false"
+    required
+  />
+  <.input
+    field={f[:password_confirmation]}
+    type="password"
+    label="Confirm new password"
+    autocomplete="new-password"
+    spellcheck="false"
+    required
+  />
+  <.button variant="primary" phx-disable-with="Changing...">
+    Save Password
+  </.button>
+</.form>