feat(install): --with-bridges flag emits bridges into $PWD

- Copy _bridges/ into ~/.claude/agents/_bridges/ so new-agent
  skill Phase 8 can invoke the renderer from the user fleet dir
- Add --with-bridges flag: after agents/hooks/skills install,
  invoke _bridges/emit.sh "$PWD" to render 11 bridge files
- Guard: if $PWD is the KeiSeiKit source repo itself (detected
  via ./install.sh + ./_bridges), warn and skip — avoid
  polluting the kit's own working tree
- --help prints usage block; flag parser loop supports future
  --activate-hooks coexistence without refactor

install.sh

@@ -1,6 +1,14 @@
 #!/usr/bin/env bash
 # KeiSeiKit — Constructor-Pattern Agent Kit installer
 # Idempotent: safe to re-run. Never overwrites settings.json or existing user manifests.
+#
+# Usage:
+#   ./install.sh                  # install agents + hooks + skills + bridges/
+#   ./install.sh --with-bridges   # also render cross-tool bridges into $PWD
+#                                   (AGENTS.md, .cursorrules, .cursor/rules/main.mdc,
+#                                    .github/copilot-instructions.md, Windsurf, Junie,
+#                                    Continue, Gemini, Aider, Replit — 11 files total)
+#                                   Skipped if $PWD is the KeiSeiKit repo itself.
 
 set -euo pipefail
 
@@ -10,6 +18,17 @@ AGENTS_DIR="$HOME_DIR/.claude/agents"
 HOOKS_DIR="$HOME_DIR/.claude/hooks"
 SKILLS_DIR="$HOME_DIR/.claude/skills"
 
+WITH_BRIDGES=0
+for arg in "$@"; do
+  case "$arg" in
+    --with-bridges) WITH_BRIDGES=1 ;;
+    --help|-h)
+      sed -n '3,11p' "${BASH_SOURCE[0]}" | sed 's/^# \{0,1\}//'
+      exit 0
+      ;;
+  esac
+done
+
 say() { printf '\033[1;36m[install]\033[0m %s\n' "$*"; }
 warn() { printf '\033[1;33m[warn]\033[0m %s\n' "$*"; }
 err() { printf '\033[1;31m[error]\033[0m %s\n' "$*" >&2; }
@@ -82,6 +101,17 @@ say "copying shared blocks -> $AGENTS_DIR/_blocks/"
 backup_dir "$AGENTS_DIR/_blocks"
 cp -f "$KIT_DIR/_blocks/"*.md "$AGENTS_DIR/_blocks/"
 
+# --- copy bridges (overwrite; templates are SSoT from kit) -----------------
+if [[ -d "$KIT_DIR/_bridges" ]]; then
+  say "copying bridge templates -> $AGENTS_DIR/_bridges/"
+  mkdir -p "$AGENTS_DIR/_bridges"
+  backup_dir "$AGENTS_DIR/_bridges"
+  cp -f "$KIT_DIR/_bridges/"*.tmpl "$AGENTS_DIR/_bridges/"
+  cp -f "$KIT_DIR/_bridges/README.md" "$AGENTS_DIR/_bridges/"
+  cp -f "$KIT_DIR/_bridges/emit.sh" "$AGENTS_DIR/_bridges/emit.sh"
+  chmod +x "$AGENTS_DIR/_bridges/emit.sh"
+fi
+
 # --- copy generic manifests, DO NOT overwrite user's existing manifests -----
 say "copying generic manifests -> $AGENTS_DIR/_manifests/ (skip if exists)"
 copied=0; skipped=0
@@ -145,6 +175,16 @@ fi
 say "generating agent .md files (--in-place)"
 AGENT_ROOT="$AGENTS_DIR" "$AGENTS_DIR/_assembler/target/release/assemble" --in-place
 
+# --- optional: render cross-tool bridges into $PWD -------------------------
+if [[ "$WITH_BRIDGES" == "1" ]]; then
+  if [[ -f "./install.sh" && -d "./_bridges" ]]; then
+    warn "not generating bridges — you are in the KeiSeiKit repo, not a project directory"
+  else
+    say "rendering cross-tool bridges into $PWD"
+    "$KIT_DIR/_bridges/emit.sh" "$PWD"
+  fi
+fi
+
 # --- done -----------------------------------------------------------------
 echo
 say "install complete"