fix: use cd + worktree inside parent dir instead of --dir flag

Issue #105: opencode run --fork/--continue --dir <path> fails to create sessions

Root cause: The --dir flag breaks session creation in opencode. Sessions
fail to be created when --dir is used with --fork or --continue.

Solution: Instead of using --dir flag, create worktrees inside the parent
session's directory and use 'cd $worktree_path && opencode run ...' to
change directory before running opencode.

Key changes:
- Worktrees now created at $PWD/.kugetsu-worktrees/{issue-ref}/ instead
  of $WORKTREES_DIR/{issue-ref}/
- .kugetsu-worktrees is a hidden directory (git ignored by default)
- cmd_start and cmd_continue now use 'cd && opencode run' instead of
  'opencode run --dir'

This approach works because:
1. Worktree is inside parent's directory tree (permission granted)
2. cd properly changes working directory before opencode runs
3. Session gets created with correct directory set
4. No .gitignore entry needed (. prefix makes it hidden from git)

skills/kugetsu/scripts/kugetsu

@@ -146,8 +146,9 @@ issue_ref_to_worktree_name() {
 
 issue_ref_to_worktree_path() {
     local issue_ref="$1"
+    local parent_dir="${2:-$WORKTREES_DIR}"
     local worktree_name=$(issue_ref_to_worktree_name "$issue_ref")
-    echo "$WORKTREES_DIR/$worktree_name"
+    echo "$parent_dir/.kugetsu-worktrees/$worktree_name"
 }
 
 issue_ref_to_branch_name() {
@@ -195,13 +196,15 @@ get_repo_url() {
 
 worktree_exists() {
     local issue_ref="$1"
-    local worktree_path=$(issue_ref_to_worktree_path "$issue_ref")
+    local parent_dir="${2:-$PWD}"
+    local worktree_path=$(issue_ref_to_worktree_path "$issue_ref" "$parent_dir")
     [ -d "$worktree_path" ]
 }
 
 create_worktree() {
     local issue_ref="$1"
-    local worktree_path=$(issue_ref_to_worktree_path "$issue_ref")
+    local parent_dir="${2:-$PWD}"
+    local worktree_path=$(issue_ref_to_worktree_path "$issue_ref" "$parent_dir")
     local branch_name=$(issue_ref_to_branch_name "$issue_ref")
     local repo_url=$(get_repo_url "$issue_ref")
     
@@ -211,9 +214,10 @@ create_worktree() {
         exit 1
     fi
     
-    ensure_worktree_dir
+    local worktree_parent_dir=$(dirname "$worktree_path")
+    mkdir -p "$worktree_parent_dir"
     
-    if worktree_exists "$issue_ref"; then
+    if worktree_exists "$issue_ref" "$parent_dir"; then
         echo "Removing existing worktree at '$worktree_path'..."
         git worktree remove "$worktree_path" 2>/dev/null || rm -rf "$worktree_path"
     fi
@@ -234,9 +238,10 @@ create_worktree() {
 
 remove_worktree_for_issue() {
     local issue_ref="$1"
-    local worktree_path=$(issue_ref_to_worktree_path "$issue_ref")
+    local parent_dir="${2:-$PWD}"
+    local worktree_path=$(issue_ref_to_worktree_path "$issue_ref" "$parent_dir")
     
-    if worktree_exists "$issue_ref"; then
+    if worktree_exists "$issue_ref" "$parent_dir"; then
         echo "Removing worktree at '$worktree_path'..."
         git worktree remove "$worktree_path" 2>/dev/null || rm -rf "$worktree_path"
     fi
@@ -1215,8 +1220,9 @@ cmd_start() {
         exit 1
     fi
 
-    local worktree_path=$(issue_ref_to_worktree_path "$issue_ref")
+    local parent_dir="$PWD"
-    create_worktree "$issue_ref"
+    local worktree_path=$(issue_ref_to_worktree_path "$issue_ref" "$parent_dir")
+    create_worktree "$issue_ref" "$parent_dir"
 
     local session_file="$(issue_ref_to_filename "$issue_ref").json"
 
@@ -1233,66 +1239,44 @@ cmd_start() {
     if [ "$active_count" -ge "$MAX_CONCURRENT_AGENTS" ]; then
         echo "Error: Max concurrent agents ($MAX_CONCURRENT_AGENTS) reached" >&2
         echo "Active sessions: $active_count" >&2
-        remove_worktree_for_issue "$issue_ref"
+        remove_worktree_for_issue "$issue_ref" "$parent_dir"
         exit 1
     fi
     
-    local fork_log="$SESSIONS_DIR/$session_file.fork.log"
-    
     if [ "$DEBUG_MODE" = true ]; then
-        opencode run "$message" --fork --session "$base_session_id" --dir "$worktree_path" 2>&1 | tee "$fork_log" &
+        (cd "$worktree_path" && opencode run "$message" --fork --session "$base_session_id" 2>&1) | tee "$SESSIONS_DIR/$session_file.debug.log" &
     else
-        opencode run "$message" --fork --session "$base_session_id" --dir "$worktree_path" >> "$fork_log" 2>&1 &
+        (cd "$worktree_path" && opencode run "$message" --fork --session "$base_session_id" 2>&1) &
     fi
 
-    local fork_pid=$!
+    # Wait briefly for session to be created
+    sleep 1
 
-    local max_attempts=10
+    # Find the new session by comparing before/after lists
-    local attempt=1
+    # Skip any session that existed before the fork and skip base/pm-agent
     local new_session_id=""
+    while IFS= read -r sess; do
+        # Skip base and pm-agent
+        [ "$sess" = "$base_session_id" ] && continue
+        [ "$sess" = "$pm_agent_session_id" ] && continue
         
-    while [ $attempt -le $max_attempts ]; do
+        # Check if this session existed before
-        sleep 1
+        local existed_before=false
-        
+        for before_sess in "${before_sessions[@]}"; do
-        if ! kill -0 $fork_pid 2>/dev/null; then
+            if [ "$sess" = "$before_sess" ]; then
-            if [ -s "$fork_log" ]; then
+                existed_before=true
-                echo "Fork command exited. Log output:" >&2
-                tail -20 "$fork_log" >&2
-            fi
-            break
-        fi
-        
-        while IFS= read -r sess; do
-            [ "$sess" = "$base_session_id" ] && continue
-            [ "$sess" = "$pm_agent_session_id" ] && continue
-            
-            local existed_before=false
-            for before_sess in "${before_sessions[@]}"; do
-                if [ "$sess" = "$before_sess" ]; then
-                    existed_before=true
-                    break
-                fi
-            done
-            
-            if [ "$existed_before" = false ]; then
-                new_session_id="$sess"
                 break
             fi
-        done < <(opencode session list 2>/dev/null | grep -oP '^ses_\w+')
+        done
         
-        if [ -n "$new_session_id" ]; then
+        if [ "$existed_before" = false ]; then
+            new_session_id="$sess"
             break
         fi
-        
+    done < <(opencode session list 2>/dev/null | grep -oP '^ses_\w+')
-        attempt=$((attempt + 1))
-    done
 
     if [ -z "$new_session_id" ]; then
-        echo "Error: Could not find newly created session after ${max_attempts}s" >&2
+        echo "Error: Could not find newly created session" >&2
-        if [ -f "$fork_log" ] && [ -s "$fork_log" ]; then
-            echo "Fork log:" >&2
-            tail -30 "$fork_log" >&2
-        fi
         remove_worktree_for_issue "$issue_ref"
         exit 1
     fi
@@ -1353,9 +1337,9 @@ cmd_continue() {
     if [ -n "$worktree_path" ] && [ -d "$worktree_path" ]; then
         echo "Using worktree: $worktree_path"
         if [ "$DEBUG_MODE" = true ]; then
-            opencode run "$message" --continue --session "$opencode_session_id" --dir "$worktree_path" 2>&1 | tee "$session_path.debug.log" &
+            (cd "$worktree_path" && opencode run "$message" --continue --session "$opencode_session_id" 2>&1) | tee "$session_path.debug.log" &
         else
-            opencode run "$message" --continue --session "$opencode_session_id" --dir "$worktree_path" 2>&1 &
+            (cd "$worktree_path" && opencode run "$message" --continue --session "$opencode_session_id" 2>&1) &
         fi
     else
         if [ "$DEBUG_MODE" = true ]; then