feat(provider): add agent environment provider adapters

[drewstone]

Summary

• add the shared AgentEnvironmentProvider contract under @tangle-network/agent-interface/environment-provider
• add provider packages for Tangle Sandbox, CLI bridge, ComputeSDK, E2B, and Daytona
• add @tangle-network/agent-provider-testkit conformance checks and a changeset for all new packages

Verification

• pnpm -r check-types
• pnpm -r test
• pnpm -r build
• pnpm --filter "@tangle-network/agent-provider-*" exec npm pack --dry-run --json
• git merge-tree --write-tree origin/main HEAD