Make development overlays container-portable and execute cleanup contracts

[adrianwebb]

Problem

A real API live Compose target could not resolve the active SDK overlay because CLI linked consumer packages to absolute host paths. Inside a containerized development target, that absolute link target is unavailable. Stopping the target also left an exited Compose container because declared cleanup operations were never executed.

Required behavior

• Create package overlay links relative to each consumer so a consistently mounted workspace remains valid inside containers.
• Inject explicit session workspace-root and worktree identities into development operations.
• Execute declared setup before startup and cleanup after bounded process shutdown, including full session stop.
• Keep cleanup unprivileged, project-owned, and argument-array based.
• Add command-boundary tests and packed-install evidence.

Discovered by Platform session dev-aeef9dc6-5a2 while proving API #111 and Deployment #174.