feat: serial:/size: external matching, exclude Hyprland FALLBACK output

- external list now accepts serial: and size: prefixes; desc: matches
  serial too. Fixes docked-mode deadlock where Hyprland's synthetic
  FALLBACK output (created when the built-in is disabled by a stale
  docked config) was treated as a real external monitor, leaving the
  daemon stuck in docked after undocking.
- modes name resolution gains serial: prefix (resolveSerial).
- add -log-level flag for observability.
- add unit tests for external matching and name resolution.
- update README and example config.

internal/config/config.go

@@ -5,7 +5,9 @@ package config
 import (
 	"errors"
 	"fmt"
+	"math"
 	"os"
+	"strconv"
 	"strings"
 	"time"
 
@@ -194,9 +196,14 @@ func countEnabled(entries []MonitorEntry) int {
 }
 
 // isInternalConnector returns true if the connector name matches a known
-// internal display pattern (eDP, LVDS, DSI). These are always part of the
-// laptop or tablet and should never trigger docked mode.
+// internal display pattern (eDP, LVDS, DSI) or Hyprland's synthetic
+// "FALLBACK" output. Internal and synthetic displays are always part of the
+// laptop/tablet (or a no-display fallback) and should never trigger docked
+// mode.
 func isInternalConnector(name string) bool {
+	if strings.EqualFold(name, "fallback") {
+		return true
+	}
 	prefixes := []string{"eDP-", "LVDS-", "DSI-", "EDP-"}
 	for _, p := range prefixes {
 		if strings.HasPrefix(name, p) {
@@ -206,31 +213,85 @@ func isInternalConnector(name string) bool {
 	return false
 }
 
+// ExternalMonitor carries the identity of a detected monitor so the
+// external list can match by name, description, serial, or resolution.
+type ExternalMonitor struct {
+	Name        string
+	Description string
+	Serial      string
+	Width       int
+	Height      int
+	RefreshRate float64
+}
+
 // MatchesExternal checks whether a monitor matches the External list.
 // Supports match modes:
 //
-//   - Plain name: exact match against name
-//   - desc: prefix: substring match against description
+//   - Plain name: exact match against the connector name
+//   - desc: prefix: substring match against description or serial
+//   - serial: prefix: substring match against serial
+//   - size:WxH / size:WxH@R: exact pixel dimensions, optionally plus
+//     refresh rate (within ±1 Hz)
 //
 // When the External list is empty, any monitor that is not an internal
-// display connector (eDP-, LVDS-, DSI-) is automatically external.
-func (c *Config) MatchesExternal(name, description string) bool {
+// display connector (eDP-, LVDS-, DSI-) or synthetic output (FALLBACK)
+// is automatically external.
+func (c *Config) MatchesExternal(m ExternalMonitor) bool {
 	if len(c.External) == 0 {
-		return !isInternalConnector(name)
+		return !isInternalConnector(m.Name)
 	}
 
 	for _, ext := range c.External {
 		switch {
 		case strings.HasPrefix(ext, "desc:"):
-			desc := strings.TrimPrefix(ext, "desc:")
-			if strings.Contains(description, desc) {
+			needle := strings.TrimPrefix(ext, "desc:")
+			if strings.Contains(m.Description, needle) || strings.Contains(m.Serial, needle) {
+				return true
+			}
+		case strings.HasPrefix(ext, "serial:"):
+			needle := strings.TrimPrefix(ext, "serial:")
+			if strings.Contains(m.Serial, needle) {
+				return true
+			}
+		case strings.HasPrefix(ext, "size:"):
+			if matchSize(ext, m.Width, m.Height, m.RefreshRate) {
 				return true
 			}
 		default:
-			if name == ext {
+			if m.Name == ext {
 				return true
 			}
 		}
 	}
 	return false
 }
+
+// matchSize reports whether a monitor matches a "size:WxH" or "size:WxH@R"
+// spec by exact pixel dimensions and, when a refresh rate is given, by
+// refresh rate within ±1 Hz.
+func matchSize(spec string, width, height int, refresh float64) bool {
+	spec = strings.TrimPrefix(spec, "size:")
+
+	parts := strings.Split(spec, "@")
+	dimParts := strings.Split(parts[0], "x")
+	if len(dimParts) != 2 {
+		return false
+	}
+
+	w, errW := strconv.Atoi(strings.TrimSpace(dimParts[0]))
+	h, errH := strconv.Atoi(strings.TrimSpace(dimParts[1]))
+	if errW != nil || errH != nil {
+		return false
+	}
+	if w != width || h != height {
+		return false
+	}
+
+	if len(parts) == 2 {
+		r, err := strconv.ParseFloat(strings.TrimSpace(parts[1]), 64)
+		if err != nil || math.Abs(r-refresh) > 1.0 {
+			return false
+		}
+	}
+	return true
+}