refactor: extract EdgeType enum to eliminate edge-type if/else chains

Introduces EdgeType.java — a Java enum that centralises the five
relationship categories (Friend, Classmate, Familiar Stranger,
Stranger, Study Group) with their:
  - File code strings ('f', 'fs', 'c', 's', 'sg')
  - Display labels
  - Colours
  - Default duration/meeting thresholds

Refactored in Main.java:
  - Edge classification in addGraph(): replaced 5-branch if/else
    with EdgeType.fromCode() lookup + getEdgeList() helper
  - Edge paint transformer: replaced 5-branch color if/else with
    EdgeType.colorForCode() single call
  - Vertex paint transformer: replaced 5 counter variables + 7-branch
    if/else with Set<EdgeType> + iterator().next().getColor()
  - getDominantLabel(): replaced 5-branch if/else with EdgeType lookup
  - Stats panel & category panel label colours: replaced FRIEND_COLOR
    etc. constants with EdgeType.FRIEND.getColor() etc.
  - JSlider default values: replaced scattered threshold constants with
    EdgeType.getDefaultDurationThreshold()/getDefaultMeetingThreshold()

Removed from Main.java:
  - 5 colour constants (FRIEND_COLOR, FS_COLOR, etc.)
  - 10 threshold constants (FRIEND_DUR_THRESHOLD, etc.)
  - 5 fLabelled/fsLabelled/etc. boolean tracking fields
  - Multiple cascading if/else chains (replaced by enum lookups)

New helpers in Main.java:
  - getEdgeList(EdgeType): maps enum to the corresponding edge list
  - isEdgeTypeVisible(String): maps type code to checkbox state

Net effect: -113 lines from Main.java, all edge-type knowledge
centralised in one enum. Adding a new relationship type now requires
adding one enum constant instead of editing 8+ places.

Author: sauravbhattacharya001

Gvisual/src/gvisual/EdgeType.java

@@ -0,0 +1,97 @@
+package gvisual;
+
+import java.awt.Color;
+
+/**
+ * Enumeration of edge relationship categories in the graph.
+ *
+ * <p>Centralises the code string, display label, colour, and default
+ * threshold values that were previously scattered across Main.java as
+ * parallel if/else chains and separate constant fields.</p>
+ *
+ * <p>Usage:</p>
+ * <pre>
+ *   EdgeType type = EdgeType.fromCode("f");   // FRIEND
+ *   Color c = type.getColor();                // Color.GREEN
+ *   String label = type.getDisplayLabel();    // "friend"
+ * </pre>
+ */
+public enum EdgeType {
+
+    FRIEND      ("f",  "friend",            Color.GREEN,             10, 2),
+    CLASSMATE   ("c",  "Classmate",         Color.BLUE,              30, 1),
+    FAMILIAR    ("fs", "Familiar Stranger",  Color.GRAY,              2, 1),
+    STRANGER    ("s",  "Stranger",           Color.RED,               2, 2),
+    STUDY_GROUP ("sg", "Study Groups",       Color.ORANGE,           20, 1);
+
+    private final String code;
+    private final String displayLabel;
+    private final Color color;
+    private final int defaultDurationThreshold;
+    private final int defaultMeetingThreshold;
+
+    EdgeType(String code, String displayLabel, Color color,
+             int defaultDurationThreshold, int defaultMeetingThreshold) {
+        this.code = code;
+        this.displayLabel = displayLabel;
+        this.color = color;
+        this.defaultDurationThreshold = defaultDurationThreshold;
+        this.defaultMeetingThreshold = defaultMeetingThreshold;
+    }
+
+    /** Returns the short code used in data files (e.g. "f", "fs", "c"). */
+    public String getCode() {
+        return code;
+    }
+
+    /** Returns the human-readable label for graph legends. */
+    public String getDisplayLabel() {
+        return displayLabel;
+    }
+
+    /** Returns the default edge colour for rendering. */
+    public Color getColor() {
+        return color;
+    }
+
+    /** Returns the default duration-of-meeting threshold (minutes). */
+    public int getDefaultDurationThreshold() {
+        return defaultDurationThreshold;
+    }
+
+    /** Returns the default number-of-meetings threshold. */
+    public int getDefaultMeetingThreshold() {
+        return defaultMeetingThreshold;
+    }
+
+    /**
+     * Looks up an {@code EdgeType} by its file code string.
+     *
+     * @param code the edge type code ("f", "fs", "c", "s", "sg")
+     * @return the matching {@code EdgeType}, or {@code null} if unknown
+     */
+    public static EdgeType fromCode(String code) {
+        if (code == null) {
+            return null;
+        }
+        String lower = code.toLowerCase();
+        for (EdgeType t : values()) {
+            if (t.code.equals(lower)) {
+                return t;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Returns the colour for a given edge type code.
+     * Falls back to {@link Color#RED} (stranger) for unknown codes.
+     *
+     * @param typeCode the edge type code
+     * @return the associated colour
+     */
+    public static Color colorForCode(String typeCode) {
+        EdgeType t = fromCode(typeCode);
+        return t != null ? t.color : Color.RED;
+    }
+}