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.

The issue lists the files to update, including docs/, versioned_docs/, CI workflows, and config files like docusaurus.config.ts and sidebars.ts. Start by searching for 'miden-base' and 'miden-node' in the repository to locate all occurrences. Focus on updating GitHub URLs, internal doc links, directory references, and CI workflow steps. Verify changes by building the docs locally to ensure links work correctly.

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