[codex] Make Likeable standalone on local workspaces

[vyakymenko]

What changed

• Replaced the Fibe runtime gateway with a local workspace engine backed by droplet filesystem storage.
• Added OpenAI Responses API generation using openai_api_key / OPENAI_API_KEY and configurable openai_model.
• Served project previews from Likeable at /api/projects/:id/preview/, with path traversal and metadata-directory protections.
• Updated ZIP/GitHub export to read local workspace source and exclude .likeable runtime metadata.
• Updated Admin/frontend config, Docker Compose, env examples, and README for standalone droplet deployment.

Validation

• go test ./cmd/likeable ./internal/workspace ./internal/project ./internal/store
• go test ./internal/likeable -run 'TestProjectPreviewServesLocalWorkspaceAndBlocksReservedPaths|TestZipDirectorySkipsWorkspaceMetadata|TestRetryProjectProvisionLaterRequiresProvisionedResources'
• npm run lint
• npm run build
• docker compose config

Known follow-up

The legacy full go test ./internal/likeable suite still contains Fibe fake CLI / Fibe HTTP assumptions and needs a separate rewrite for the standalone workspace engine.