feat: add Codex CLI as a first-class fourth platform

Rebuilt from scratch following Codex CLI's actual architecture (as
outlined in the review on PR #26). Closes the integration gap with a
proper build adapter, correct install paths, TOML agent files, and
all the architectural differences documented and tested.

What changed vs the previous attempt (PR #26):

- Agents: build adapter generates .toml files (name/description/
  developer_instructions) into dist/codex-cli/.codex/agents/ instead
  of copying .md files with sed transforms
- Skills: installed to .agents/skills/ (correct Codex discovery path)
  instead of .codex/skills/
- Dispatcher: AGENTS.md uses a root-context orchestration header that
  works within agents.max_depth=1 constraints; named-agent routing
  replaced with embedded-instructions workaround for the known
  spawn_agents limitation (openai/codex#15250)
- Tool compat: AskUserQuestion and request_user_input removed; all
  prompts adapted to Codex's actual tool set and approval/confirmation
  flow
- Installer/updater: launchme.sh --platform codex-cli and updateme.sh
  with Codex auto-detection, creating the correct split layout
  (AGENTS.md + .codex/agents/ + .codex/config.toml + .agents/skills/)
- Tests: new per-adapter test suite (tests/adapters/codex-cli/),
  install/update smoke (tests/scripts/codex-cli-install.test.sh), and
  a four-platform parity gate that proves Codex changes do not regress
  Claude Code, Gemini CLI, or OpenCode
- Docs: new codex-cli.md guide, codex-migration.md for users switching
  from other platforms, and README/getting-started/examples updated for
  four-platform positioning
- Bash harness: .gitattributes added to enforce LF on .sh files;
  harness LF-normalized so tests/run.sh works on Windows checkouts
- .gitignore: .planning/ added (internal GSD workflow artifacts)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/lib.sh

@@ -51,6 +51,20 @@ copy_if_changed() {
   fi
 }
 
+# ── copy_tree_if_changed <src_dir> <dst_dir> ────────────────────────────────
+# Overlays a source directory tree onto the destination when files differ or
+# the destination does not exist. This preserves nested skill assets/scripts
+# needed by platforms such as Codex CLI.
+copy_tree_if_changed() {
+  local src="$1" dst="$2"
+  _LAST_CHANGED=0
+  if [[ ! -d "$dst" ]] || ! diff -qr "$src" "$dst" >/dev/null 2>&1; then
+    mkdir -p "$dst"
+    cp -R "$src/." "$dst/"
+    _LAST_CHANGED=1
+  fi
+}
+
 # ── _insert_after_start_marker <dst> <content> ───────────────────────────────
 # Inserts <content> immediately after the MBIFC:CUSTOM_AGENTS_START line in dst.
 # dst must already exist and contain the marker.
@@ -304,7 +318,32 @@ install_agents() {
   local src_dir="$1" dst_dir="$2"
   local count=0 manifest=()
   mkdir -p "$dst_dir"
-  for src in "$src_dir/"*.md; do
+  for src in "$src_dir/"*; do
+    [[ -f "$src" ]] || continue
+    case "$src" in
+      *.md|*.toml) ;;
+      *) continue ;;
+    esac
+    local name; name="$(basename "$src")"
+    manifest+=("$name")
+    copy_if_changed "$src" "$dst_dir/$name"
+    if [[ $_LAST_CHANGED -eq 1 ]]; then
+      [[ $VERBOSE_COPY -eq 1 ]] && info "Updated agent: $name" || true
+      count=$((count + 1))
+    fi
+  done
+  manifest_write "agents" "${manifest[@]}"
+  printf '%d' "$count"
+}
+
+# install_toml_agents <src_dir> <dst_dir>
+# Copies *.toml agent files from src to dst. Used by Codex CLI platform installs
+# where agents are .toml rather than .md. Tracked in the manifest under "agents".
+install_toml_agents() {
+  local src_dir="$1" dst_dir="$2"
+  local count=0 manifest=()
+  mkdir -p "$dst_dir"
+  for src in "$src_dir/"*.toml; do
     [[ -f "$src" ]] || continue
     local name; name="$(basename "$src")"
     manifest+=("$name")
@@ -349,8 +388,7 @@ install_skills() {
     [[ -f "${skill_src}SKILL.md" ]] || continue
     local name; name="$(basename "$skill_src")"
     manifest+=("$name")
-    mkdir -p "$dst_dir/$name"
-    copy_if_changed "${skill_src}SKILL.md" "$dst_dir/$name/SKILL.md"
+    copy_tree_if_changed "$skill_src" "$dst_dir/$name"
     if [[ $_LAST_CHANGED -eq 1 ]]; then
       [[ $VERBOSE_COPY -eq 1 ]] && info "Updated skill: $name" || true
       count=$((count + 1))