feat: add OPER command and oper-only WHOIS client info

- Add OPER command with NEOIRC_OPER_NAME/NEOIRC_OPER_PASSWORD config
- Add is_oper column to sessions table
- Add RPL_WHOISACTUALLY (338): show client IP/hostname to opers
- Add RPL_WHOISOPERATOR (313): show oper status in WHOIS
- Add GetOperCount for accurate LUSERS oper count
- Fix README schema: add ip/is_oper to sessions, ip/hostname to clients
- Add OPER command documentation and numeric references to README
- Refactor executeWhois to stay under funlen limit
- Add comprehensive tests for OPER auth, oper WHOIS, non-oper WHOIS

Closes #81

internal/db/queries.go

@@ -298,6 +298,75 @@ func (database *Database) GetClientHostInfo(
 	return &info, nil
 }
 
+// SetSessionOper sets the is_oper flag on a session.
+func (database *Database) SetSessionOper(
+	ctx context.Context,
+	sessionID int64,
+	isOper bool,
+) error {
+	val := 0
+	if isOper {
+		val = 1
+	}
+
+	_, err := database.conn.ExecContext(
+		ctx,
+		`UPDATE sessions SET is_oper = ? WHERE id = ?`,
+		val, sessionID,
+	)
+	if err != nil {
+		return fmt.Errorf("set session oper: %w", err)
+	}
+
+	return nil
+}
+
+// IsSessionOper returns whether the session has oper
+// status.
+func (database *Database) IsSessionOper(
+	ctx context.Context,
+	sessionID int64,
+) (bool, error) {
+	var isOper int
+
+	err := database.conn.QueryRowContext(
+		ctx,
+		`SELECT is_oper FROM sessions WHERE id = ?`,
+		sessionID,
+	).Scan(&isOper)
+	if err != nil {
+		return false, fmt.Errorf(
+			"check session oper: %w", err,
+		)
+	}
+
+	return isOper != 0, nil
+}
+
+// GetLatestClientForSession returns the IP and hostname
+// of the most recently created client for a session.
+func (database *Database) GetLatestClientForSession(
+	ctx context.Context,
+	sessionID int64,
+) (*ClientHostInfo, error) {
+	var info ClientHostInfo
+
+	err := database.conn.QueryRowContext(
+		ctx,
+		`SELECT ip, hostname FROM clients
+		 WHERE session_id = ?
+		 ORDER BY created_at DESC LIMIT 1`,
+		sessionID,
+	).Scan(&info.IP, &info.Hostname)
+	if err != nil {
+		return nil, fmt.Errorf(
+			"get latest client for session: %w", err,
+		)
+	}
+
+	return &info, nil
+}
+
 // GetChannelByName returns the channel ID for a name.
 func (database *Database) GetChannelByName(
 	ctx context.Context,
@@ -951,6 +1020,26 @@ func (database *Database) GetUserCount(
 	return count, nil
 }
 
+// GetOperCount returns the number of sessions with oper
+// status.
+func (database *Database) GetOperCount(
+	ctx context.Context,
+) (int64, error) {
+	var count int64
+
+	err := database.conn.QueryRowContext(
+		ctx,
+		"SELECT COUNT(*) FROM sessions WHERE is_oper = 1",
+	).Scan(&count)
+	if err != nil {
+		return 0, fmt.Errorf(
+			"get oper count: %w", err,
+		)
+	}
+
+	return count, nil
+}
+
 // ClientCountForSession returns the number of clients
 // belonging to a session.
 func (database *Database) ClientCountForSession(