feat(studio): add reusable environment sources and sharing

[evanlowe]

Summary

• add public Git repository discovery with Dockerfile selection and CodePipeline builds
• add regional Container Registry image selection by instance, namespace, repository, and tag
• add compact environment share codes, clipboard detection, batch import, and deletion
• preserve image, tool, cloud resource, Git/CR, and Skill data during deep-copy import
• reject cross-provider imports and harden Git discovery against SSRF and DNS rebinding

Validation

• pre-commit: passed
• frontend tests: 934 passed
• environment backend tests: 103 passed
• full Python suite: 3148 passed, 5 skipped; 2 transient debug-server startup timeouts passed when rerun in isolation
• packaged WebUI asset verification: 85 files / 229 references
• production frontend build: passed
• local end-to-end: batch-imported three ANR environments into test and invoked all three through Agent environment mounts
• visual QA: desktop 1440x900 and mobile 390x844, including list, import, and share states