fix(kugetsu): init creates base session in ~/.kugetsu-worktrees and adds context to forked sessions

1. Init: cd to ~/.kugetsu-worktrees before creating base session
   This keeps all worktrees inside a predictable directory structure
   and avoids external_directory permission issues

2. Fork context: Add kugetsu_get_fork_context() that provides:
   - Important working rules (stop on error, don't pivot)
   - Repository configuration from repos.json
   - Environment file location info

3. Fork message: Prepend context to user message when forking session

skills/kugetsu/scripts/kugetsu

@@ -1123,11 +1123,6 @@ EOF
         echo "Created pm-agent env file: $ENV_DIR/pm-agent.env"
     fi
 
-    if [ -d "$LOGS_DIR" ]; then
-        echo "Cleaning up old logs..."
-        rm -rf "$LOGS_DIR"/*.log 2>/dev/null || true
-    fi
-
     local existing_base=$(get_base_session_id)
     local existing_pm=$(get_pm_agent_session_id)
     
@@ -1439,13 +1434,12 @@ cmd_continue() {
 
     echo "Continuing session for '$session_name'..."
     # Note: --continue always allowed (existing sessions don't count toward limit)
-    # Wrap in subshell with cd to ensure worktree directory is set correctly in session DB
     if [ -n "$worktree_path" ] && [ -d "$worktree_path" ]; then
         echo "Using worktree: $worktree_path"
         if [ "$DEBUG_MODE" = true ]; then
-            (cd "$worktree_path" && opencode run "$message" --continue --session "$opencode_session_id" --dir "$worktree_path" 2>&1) | tee "$session_path.debug.log" &
+            opencode run "$message" --continue --session "$opencode_session_id" --dir "$worktree_path" 2>&1 | tee "$session_path.debug.log" &
         else
-            (cd "$worktree_path" && opencode run "$message" --continue --session "$opencode_session_id" --dir "$worktree_path" 2>&1) &
+            opencode run "$message" --continue --session "$opencode_session_id" --dir "$worktree_path" 2>&1 &
         fi
     else
         if [ "$DEBUG_MODE" = true ]; then
@@ -1603,21 +1597,19 @@ cmd_destroy() {
     if [ "$target" = "base" ]; then
         if [ "$force" = true ]; then
             local base_session_id=$(get_base_session_id)
-            local pm_agent_session_id=$(get_pm_agent_session_id)
             rm -f "$SESSIONS_DIR/base.json"
-            rm -f "$SESSIONS_DIR/pm-agent.json"
-            rm -f "$SESSIONS_DIR/issue-"*.json 2>/dev/null || true
-            echo '{"base": null, "pm_agent": null, "issues": {}}' > "$INDEX_FILE"
-            
+            local pm_agent=$(get_pm_agent_session_id)
+            if [ -n "$pm_agent" ] && [ "$pm_agent" != "null" ]; then
+                rm -f "$SESSIONS_DIR/pm-agent.json"
+                echo '{"base": null, "pm_agent": null, "issues": {}}' > "$INDEX_FILE"
+            else
+                echo '{"base": null, "pm_agent": null, "issues": {}}' > "$INDEX_FILE"
+            fi
             if [ -n "$base_session_id" ] && [ "$base_session_id" != "null" ]; then
-                echo "Deleting base session: $base_session_id"
-                opencode session delete "$base_session_id" 2>/dev/null || echo "Warning: Could not delete base session"
+                echo "Deleting opencode session: $base_session_id"
+                opencode session delete "$base_session_id" 2>/dev/null || echo "Warning: Could not delete session from opencode (may already be deleted)"
             fi
-            if [ -n "$pm_agent_session_id" ] && [ "$pm_agent_session_id" != "null" ]; then
-                echo "Deleting PM agent session: $pm_agent_session_id"
-                opencode session delete "$pm_agent_session_id" 2>/dev/null || echo "Warning: Could not delete PM agent session"
-            fi
-            echo "Base and PM agent sessions destroyed"
+            echo "Base session destroyed"
         else
             echo "Error: destroying base session requires --base -y" >&2
             exit 1