along-plan v1.0.0 released

- Introduces a read-only planning phase for safe code analysis.
- Enforces exploration using only non-destructive tools (`read`, `grep`, `glob`, safe `bash` as per allowlist).
- Produces a numbered plan under a `Plan:` header.
- Saves the plan to a Markdown file with checklist steps and acceptance criteria.
- Uses `[DONE:n]` markers to track step completion during execution.