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/db/users.go

@@ -80,6 +80,17 @@ func (d *DB) SetPassword(username, password string) error {
 	return requireRowsAffected(res, ErrUserNotFound)
 }
 
+// SetProfile updates username's display name and email address. Returns
+// ErrUserNotFound if the user doesn't exist.
+func (d *DB) SetProfile(username, displayName, email string) error {
+	res, err := d.conn.Exec(`UPDATE users SET display_name = ?, email = ? WHERE username = ?`, displayName, email, username)
+	if err != nil {
+		return fmt.Errorf("setting profile: %w", err)
+	}
+	return requireRowsAffected(res, ErrUserNotFound)
+}
+
+
 // DeleteUser removes username along with all of its calendars, address
 // books, and sharing grants (calendars/addressbooks cascade via foreign
 // key; shares are cleaned up explicitly since they reference usernames as