docs: update references for miden-base → protocol and miden-node → node repo renames

Two repos have been renamed:
- `miden-base` → `protocol`
- `miden-node` → `node`

The docs still reference the old names in ~86 files across URLs, prose, CI workflows, config, and internal links.

## Scope breakdown

| Area | miden-base | miden-node |
|------|-----------|-----------|
| Active docs (`docs/`) | 8 files | 1 file |
| Versioned docs | ~20 files | ~15 files |
| CI workflows | 2 files (~20 lines each) | 2 files (~20 lines each) |
| Config (docusaurus, sidebars, release-manifest) | 3 files | 3 files |
| README | 1 file | 1 file |

## Key areas

- GitHub URLs (`0xMiden/miden-base` → `0xMiden/protocol`, `0xMiden/miden-node` → `0xMiden/node`)
- Internal doc links (`/design/miden-base/` → `/design/protocol/`, `/design/miden-node/` → `/design/node/`)
- Directory names under `docs/design/` and `versioned_docs/`
- CI workflow env vars and checkout steps
- `release-manifest.yml` repo keys
- `docusaurus.config.ts` redirect rules
- `sidebars.ts` comments

## Note

Versioned docs snapshots (v0.11, v0.12) may keep old names since they reflect historical state.