refactor: modularize kugetsu shell script

Split the monolithic kugetsu script into modular components:

Modules created:
- kugetsu-config.sh - Config/env loading and global variables
- kugetsu-index.sh - Index.json read/write via JSON
- kugetsu-worktree.sh - Git worktree operations
- kugetsu-log.sh - Structured logging and notifications
- kugetsu-session.sh - Session create/fork/destroy logic
- kugetsu-queue-daemon.sh - Queue daemon subprocess

Main script (kugetsu) is now a thin dispatcher that sources all modules.

Acceptance Criteria:
- All existing commands work exactly as before
- Main script sources modules
- Each module is independently testable

Fixes #116

skills/kugetsu/scripts/kugetsu-log.sh

@@ -0,0 +1,91 @@
+#!/bin/bash
+set -euo pipefail
+
+cmd_logs() {
+    local count="${1:-10}"
+    
+    if [ ! -d "$LOGS_DIR" ]; then
+        echo "No logs found."
+        return
+    fi
+    
+    find "$LOGS_DIR" -type f -mtime +7 -delete 2>/dev/null
+    
+    ls -lt "$LOGS_DIR" | head -$((count + 1)) | tail -$count | while read line; do
+        echo "$line"
+    done
+    
+    echo ""
+    echo "Recent log contents:"
+    echo "===================="
+    
+    for log in $(ls -lt "$LOGS_DIR" | head -$((count + 1)) | tail -$count | awk '{print $NF}'); do
+        if [ -f "$LOGS_DIR/$log" ]; then
+            echo ""
+            echo "--- $log ---"
+            tail -20 "$LOGS_DIR/$log" | while read line; do
+                echo "  $(mask_sensitive_vars "$line")"
+            done
+        fi
+    done
+}
+
+kugetsu_add_notification() {
+    local notification_type="$1"
+    local message="$2"
+    local issue_ref="${3:-}"
+    local timestamp=$(date -Iseconds)
+    
+    mkdir -p "$(dirname "$NOTIFICATIONS_FILE")"
+    
+    local notifications="[]"
+    if [ -f "$NOTIFICATIONS_FILE" ]; then
+        notifications=$(cat "$NOTIFICATIONS_FILE")
+    fi
+    
+    local new_notification=$(python3 -c "import json; print(json.dumps({
+        'type': '$notification_type',
+        'message': '$message',
+        'issue_ref': '$issue_ref',
+        'timestamp': '$timestamp',
+        'read': False
+    }))")
+    
+    notifications=$(python3 -c "import json; n=json.loads('$notifications'); n.append(json.loads('$new_notification')); print(json.dumps(n[-50:] if len(n)>50 else n, indent=2))")
+    
+    echo "$notifications" > "$NOTIFICATIONS_FILE"
+}
+
+cmd_notify() {
+    local action="${1:-list}"
+    
+    case "$action" in
+        list)
+            if [ ! -f "$NOTIFICATIONS_FILE" ]; then
+                echo "No notifications."
+                return
+            fi
+            
+            local notifications=$(cat "$NOTIFICATIONS_FILE")
+            local count=$(echo "$notifications" | python3 -c "import sys, json; n=json.load(sys.stdin); print(sum(1 for x in n if not x.get('read', False)))")
+            
+            if [ "$count" -eq 0 ]; then
+                echo "No unread notifications."
+                return
+            fi
+            
+            echo "Unread notifications ($count):"
+            echo "$notifications" | python3 -c "import sys, json; [print(f\"  [{x.get('timestamp', '')}] {x.get('type', '')}: {x.get('message', '')}\") for x in json.load(sys.stdin) if not x.get('read', False)]"
+            ;;
+        clear)
+            if [ -f "$NOTIFICATIONS_FILE" ]; then
+                python3 -c "import json; print(json.dumps([x for x in json.load(open('$NOTIFICATIONS_FILE')) if x.get('read', False)], indent=2))" > "$NOTIFICATIONS_FILE"
+                echo "Cleared unread notifications."
+            fi
+            ;;
+        *)
+            echo "Usage: kugetsu notify [list|clear]" >&2
+            exit 1
+            ;;
+    esac
+}