Fixed relative cwd double-scoping in custom sandbox connectors

What Changed

Flue now applies a created agent's cwd exactly once during init(), relative to the connector's provider-owned base directory. SandboxFactory.createSessionEnv() now receives only { id }; connector implementations should stop consuming cwd parameter.

Operator Implication

Custom sandbox connector implementations must stop expecting cwd parameter in createSessionEnv() and update their code accordingly.

Receipt

• From CHANGELOG.md v0.9.1 (2026-06-02): 'Fixed relative cwd double-scoping in custom sandbox connectors. Flue now applies a created agent's cwd exactly once du