feat(security): workspace sandbox

[cniska]

Summary

• enforce a canonical workspace sandbox boundary across file, code, git, and scoped search tools using realpath checks and symlink-escape blocking
• add structured sandbox violations (E_SANDBOX_VIOLATION/sandbox_violation) plus lifecycle debug/trace events for sandbox root and violations
• update shell-run to argv-only execution (cmd + args), remove shell-string paths, and validate command/path-like arguments against the workspace sandbox
• remove workspace profile line-width detection and related references so formatters own line wrapping
• add workspace documentation and tests for sandbox enforcement, observability, and the updated shell-run contract

Fixes #77