chore: drop Codespaces, document localhost + Docker step-by-step

[fede-kamel]

Summary

Drop the Codespaces launch path. We're keeping two ways to run the workbench going forward — local from source and Docker — and the docs are reorganised around those two paths.

Codespaces never worked for the OCI providers (api-key or session token) because the OCI SDK signs every request with a private key on disk, and a fresh Codespace has neither ~/.oci/config nor any .pem. Trying to ship Codespaces alongside the OCI flow meant the demo path silently fell back to OpenAI / Anthropic only, which isn't representative of what locus is about.

Removed

• .devcontainer/ (4 files — devcontainer.json, postCreate.sh, welcome.md, workbench-attach.sh).
• Codespaces launch buttons, badges, billing copy from README.md, docs/index.md, docs/workbench.md.
• The .app.github.dev allowedHost rule in workbench/web/vite.config.ts.

Doc updates

• docs/workbench.md restructured into two clear sections:
  • Run it locally (from source) — prereqs (Python 3.11+, Node 20+), step-by-step git clone → pip install → three-terminal setup, make-based shortcut, plus three curl commands to verify each tier is up.
  • Run it in Docker — docker build + docker run, with both the OpenAI/Anthropic (no extra args) and OCI (-v "$HOME/.oci:$HOME/.oci:ro" -e "HOME=$HOME") variants explained. Includes a port-collision section for remapping host-side ports.
• The Docker section explains why the OCI mount + HOME pair is needed: ~/.oci/config's key_file line is an absolute host path, so mirroring $HOME/.oci at the same path inside the container is what makes the SDK find the private key.
• Provider settings entries updated — OCI providers now correctly state they work on both localhost and Docker (was "Local-machine only").
• Troubleshooting calls out the two specific Docker+OCI failure modes: missing bind-mount and missing HOME env.
• README.md collapsed to the same two paths, OCI bind-mount snippet matches.
• workbench/README.md gains a ## Run in Docker section so the in-tree reader sees the same guidance.

Verified live

• Built the workbench Docker image, ran with -v "$HOME/.oci:$HOME/.oci:ro" -e "HOME=$HOME" → /api/models against LUIGI_FRA_API in us-chicago-1 returned 112 OCI models (the SDK successfully signed requests against the bind-mounted config + key file).
• Confirmed the alternative dual-mount form (-v $HOME/.oci:/root/.oci:ro -v $HOME/.oci:$HOME/.oci:ro) also works, but the single-mount + HOME env form is cleaner.

Test plan

• grep -ri codespace returns no matches across the tracked tree.
• OCI bind-mount documented variant tested live against LUIGI_FRA_API (112 models returned).
• CI green on this PR (lint, mypy, tests on 3.11–3.14, mkdocs strict build).