Add account management page

Add a new /web/account page, reachable by clicking the username in
the nav, with two forms: updating display name/email, and changing
the password (requires the current password, min 8 chars, confirm
match). Add db.SetProfile to persist display name/email.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

internal/web/templates/layout.templ

@@ -23,7 +23,7 @@ templ Layout(title string, username string) {
 					</div>
 					if username != "" {
 						<div class="flex items-center gap-4 text-sm text-gray-600">
-							<span>{ username }</span>
+							<a href="/web/account" class="hover:text-indigo-600">{ username }</a>
 							<a href="/web/logout" class="text-red-600 hover:underline">Logout</a>
 						</div>
 					}