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>

CLAUDE.md

@@ -88,7 +88,7 @@ Position-shift pattern for panes (legacy `session_panes` table): negate-and-rest
 
 ## Environment
 
-Required: `DATABASE_URL`, `LLAMA_SWAP_URL`. Optional: `PORT` (3000), `HOST` (0.0.0.0), `PROJECT_ROOT_WHITELIST` (/opt), `DEFAULT_MODEL`, `LOG_LEVEL`.
+Required: `DATABASE_URL`, `LLAMA_SWAP_URL`. Optional: `PORT` (3000), `HOST` (0.0.0.0), `PROJECT_ROOT_WHITELIST` (/opt, read-only scope for add-existing path resolution), `BOOTSTRAP_ROOT` (/opt/projects, writable scope for create-new-project bootstrap mkdir target — host must `mkdir -p /opt/projects` before container start), `DEFAULT_MODEL`, `LOG_LEVEL`.
 
 ## Workflow