security: scope /opt mount to /opt/projects

Splits the previous /opt:/opt:rw bind into two mounts to narrow the
writable scope of the container:

- /opt:/opt:ro — read-only mount for legacy/existing project
  add-existing flow. resolveProjectPath still uses
  PROJECT_ROOT_WHITELIST (/opt by default) so existing projects under
  /opt/<name> (analytics, boolab, boocode itself) continue to resolve
  and serve their file-tree via the read-only tools.
- /opt/projects:/opt/projects:rw — writable mount targeted at the
  create-new-project bootstrap path.

Picked Option B from the spec (simpler than two scan roots):
PROJECT_ROOT_WHITELIST stays /opt, new BOOTSTRAP_ROOT env var defaults
to /opt/projects and is used by project_bootstrap.ts as the mkdir
target. Bootstrap path-escape check now compares against
BOOTSTRAP_ROOT.

Prereq: host must `mkdir -p /opt/projects` before next container
restart. Documented in CLAUDE.md and .env.example.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -9,7 +9,11 @@ services:
     environment:
       DATABASE_URL: postgres://boocode:${POSTGRES_PASSWORD}@boocode_db:5432/boocode
     volumes:
-      - /opt:/opt:rw
+      # Read-only mount for legacy/existing project add-existing flow.
+      - /opt:/opt:ro
+      # Writable mount only for the create-new-project bootstrap target.
+      # Host must `mkdir -p /opt/projects` before container start.
+      - /opt/projects:/opt/projects:rw
     depends_on:
       - boocode_db
     networks: