refactor: restructure PM role under skills/kugetsu/pm/

### Changes:

1. **Moved kugetsu-pm to skills/kugetsu/pm/SKILL.md**
   - Simplified to 79 lines (under 100 line target)
   - kugetsu v3.0 with essential PM role definition
   - PM context injected at init/start/continue time

2. **Updated kugetsu_get_pm_context()**
   - Now reads from ~/.kugetsu/pm-agent.md (user custom) first
   - Falls back to skills/kugetsu/pm/SKILL.md (default)

3. **Updated kugetsu-chat v4.0**
   - Added notification checking on status/update queries
   - When user asks "status?", "any updates?", etc., check kugetsu notify list
   - Hybrid approach: PM includes notifications + kugetsu-chat checks on status

4. **Removed old skills/kugetsu-pm/SKILL.md**
   - Replaced by skills/kugetsu/pm/SKILL.md

### Structure:
skills/kugetsu/
├── SKILL.md
├── scripts/kugetsu
├── chat/           # future: kugetsu-chat could move here
│   ├── SKILL.md
│   └── SOUL.md
└── pm/
    └── SKILL.md    # PM role definition (v3.0)

skills/kugetsu/scripts/kugetsu

@@ -307,9 +307,13 @@ check_opencode_session_exists() {
 }
 
 kugetsu_get_pm_context() {
-    local pm_context_file="${KUGETSU_DIR}/pm-agent.md"
-    if [ -f "$pm_context_file" ]; then
-        cat "$pm_context_file"
+    local user_pm_context="${KUGETSU_DIR}/pm-agent.md"
+    local skill_pm_context="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/../pm/SKILL.md"
+    
+    if [ -f "$user_pm_context" ]; then
+        cat "$user_pm_context"
+    elif [ -f "$skill_pm_context" ]; then
+        cat "$skill_pm_context"
     else
         echo ""
     fi