fix: fail conditional operations closed with Files policy

[kauandotnet]

Summary

• keep ordinary operations on the Files SDK plugin, hook, and receipt pipeline
• hide every native conditional capability when caller Files policy would be bypassed
• reject direct conditional upload, exact read, delete, and promotion before adapter dispatch
• snapshot Files hooks at construction so compatibility cannot drift through later mutation
• document the Files SDK versus NestM responsibility boundary and compatibility matrix

Current state verified

• base is @nestm/storage@0.1.0-alpha.8 at 2f2e1d2
• alpha.8 pins files-sdk 2.2.3
• Files SDK 2.2.4 and current 2.2.5 still have no native conditional operations in FilesOperation or plugin handlers
• no Files SDK dependency bump is included because neither release closes the gap

Verification

• 246 unit tests passed
• 55 end-to-end tests passed; 4 credentialed live cases skipped
• lint, formatting, and TypeScript checks passed
• build, strict publint, packed install, and packed-consumer test passed

Follow-up

This is an explicitly interim compatibility gate for #29. The permanent fix belongs upstream: native create, replace, exact-read, delete, and promotion conditions must traverse the existing Files operation/plugin/hook/receipt dispatcher without weakening provider CAS. Once that exists, this gate should be deleted instead of growing a second plugin pipeline in NestM.

R2 is out of scope.