Support Qoder environment setup scripts

[heimanba]

Summary

• add declarative config.setup_script support with a 64 KiB UTF-8 limit
• reconcile Qoder setup scripts through create, POST update, sync/export, and drift detection
• normalize Qoder response-only package fields and validate writable package/self-hosted constraints
• converge removed environment metadata with Qoder merge-patch tombstones
• document setup semantics and add an idempotent Qoder example

Why

Qoder supports sandbox setup scripts, but OpenAgentPack previously rejected or dropped the field. The Environment adapter also used the wrong update method and could round-trip response-only package fields that Qoder rejects.

Validation

• scoped verification passed
• SDK suite: 651 passed, 0 failed
• pre-push full workspace typecheck, architecture checks, and test profile passed
• live Qoder test using .env: create/read/update/drift/reconcile, metadata removal, setup-script removal/restoration, and cleanup passed
• verified no disposable Qoder probe resources remain