feat(bridges): emit.sh renderer with --only filter

- Single-concern renderer (<100 LOC per Constructor Pattern)
- Idempotent — existing files are skipped, not overwritten
- Args: <target> [name] [description]; name defaults to basename,
  description defaults to first non-blank line of CLAUDE.md or
  README.md, fallback "No description"
- --only <output-path> restricts emission to one file (used by
  /new-agent Phase 8 "AGENTS.md only" path)
- Placeholders substituted: PROJECT_NAME, PROJECT_DESCRIPTION,
  YEAR, MONTH, DATE

_bridges/emit.sh

@@ -0,0 +1,77 @@
+#!/usr/bin/env bash
+# _bridges/emit.sh — render cross-tool bridge templates into a target dir.
+# Usage:
+#   emit.sh <target-dir> [project-name] [project-description]
+#   emit.sh --only <output-path> <target-dir> [project-name] [project-description]
+# Idempotent: files that already exist are skipped, not overwritten.
+
+set -euo pipefail
+
+BRIDGES_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+ONLY=""
+if [ "${1:-}" = "--only" ]; then
+  ONLY="${2:-}"
+  [ -n "$ONLY" ] || { echo "error: --only requires an output path" >&2; exit 2; }
+  shift 2
+fi
+
+TARGET="${1:-}"
+[ -n "$TARGET" ] || { echo "usage: emit.sh [--only <path>] <target-dir> [name] [description]" >&2; exit 2; }
+[ -d "$TARGET" ] || { echo "error: target dir does not exist: $TARGET" >&2; exit 2; }
+TARGET="$(cd "$TARGET" && pwd)"
+
+NAME="${2:-$(basename "$TARGET")}"
+DESC="${3:-}"
+if [ -z "$DESC" ]; then
+  for f in "$TARGET/CLAUDE.md" "$TARGET/README.md"; do
+    if [ -f "$f" ]; then
+      DESC="$(grep -m1 -E '^[[:space:]]*[^#[:space:]].*' "$f" | sed 's/^[[:space:]]*//' || true)"
+      [ -n "$DESC" ] && break
+    fi
+  done
+  [ -n "$DESC" ] || DESC="No description"
+fi
+
+YEAR="$(date +%Y)"; MONTH="$(date +%m)"; DATE="$(date +%Y-%m-%d)"
+
+# tmpl|output-rel-path (11 entries, matches _bridges/README.md table)
+MAP="cursorrules.tmpl|.cursorrules
+agents-md.tmpl|AGENTS.md
+copilot.tmpl|.github/copilot-instructions.md
+cursor-mdc.tmpl|.cursor/rules/main.mdc
+windsurf.tmpl|.windsurf/rules/main.md
+junie.tmpl|.junie/guidelines.md
+continue.tmpl|.continue/rules/main.md
+gemini.tmpl|GEMINI.md
+aider-conventions.tmpl|CONVENTIONS.md
+aider-conf.tmpl|.aider.conf.yml
+replit.tmpl|replit.md"
+
+# sed-escape a replacement string (handles & / \ newlines)
+sed_escape() { printf '%s' "$1" | sed -e 's/[\\&/]/\\&/g' -e 's/$/\\/' -e '$ s/\\$//'; }
+
+created=0; skipped=0
+while IFS='|' read -r tmpl out; do
+  [ -n "$tmpl" ] || continue
+  [ -n "$ONLY" ] && [ "$out" != "$ONLY" ] && continue
+  src="$BRIDGES_DIR/$tmpl"
+  dst="$TARGET/$out"
+  [ -f "$src" ] || { echo "error: missing template $src" >&2; exit 3; }
+  if [ -e "$dst" ]; then
+    echo "skipped: $out (exists)"
+    skipped=$((skipped+1))
+    continue
+  fi
+  mkdir -p "$(dirname "$dst")"
+  sed -e "s/{{PROJECT_NAME}}/$(sed_escape "$NAME")/g" \
+      -e "s/{{PROJECT_DESCRIPTION}}/$(sed_escape "$DESC")/g" \
+      -e "s/{{YEAR}}/$YEAR/g" \
+      -e "s/{{MONTH}}/$MONTH/g" \
+      -e "s/{{DATE}}/$DATE/g" \
+      "$src" > "$dst"
+  echo "created: $out"
+  created=$((created+1))
+done <<< "$MAP"
+
+echo "bridges: $created created, $skipped skipped"