Add connected Doable code context plugin

[alphali]

Summary

• Add the connected Doable Code Context plugin with separate setup and question-answering Skills.
• Retire the legacy context-only upload-file plugin so coding agents cannot accidentally choose the obsolete workflow.
• During first setup, build a local private workspace/repo map and upload only a user-approved sanitized routing profile.
• Pull a frozen Doable context request, inspect the scoped mono-repo or multi-repo sources, ask the local user for clarification when necessary, and submit structured findings and opaque references directly to Doable.
• Keep repository paths, revisions, evidence locators, source snippets, secrets, and private environment data local.
• Support round-code bootstrap, deleted-local-state recovery, artifact roots, idempotent submissions, and wrong-workspace/privacy validation.

Verification

• npm test passed, including release verification and helper mock E2E.
• Codex, Claude Code, and Cursor plugin manifests validate.
• Cross-contract request fixtures validate against the TRD backend models.

Dependencies and rollout

• Backend: https://github.com/getdoable/trd/pull/380
• Schema: https://github.com/getdoable/qa-supabase/pull/114
• The repository remains private for internal testing. It must be made public, or customers must be granted access, before external installation.