v0.16.1

feat(mcp): publish sem to the official MCP registry (#446)

Publishes sem to the [official MCP
registry](https://github.com/modelcontextprotocol/registry) as
`io.github.ataraxy-labs/sem`, so MCP clients that browse the registry
(VS Code, Cursor, Claude Code, and others) can discover and install the
server directly.

## What's in here

- **`server.json`** — registry manifest: npm package
`@ataraxy-labs/sem`, stdio transport, launched as `sem mcp` via npx.
Validated against the official `2025-12-11` server schema.
- **`package.json`** — adds the `mcpName` field the registry checks
against the published npm package, and syncs the long-stale wrapper
version (0.7.0 → 0.16.1; CI re-syncs at publish anyway).
- **`release.yml`** — new `publish-mcp-registry` job after the npm
publish: stamps the release version into `server.json` with jq, logs in
with GitHub OIDC (`id-token: write`, no new repo secrets), and publishes
with `mcp-publisher`. Retries once after 60s in case the npm publish
hasn't propagated when the registry validates `mcpName`.
- **Version bump 0.16.0 → 0.16.1** across the workspace crates +
lockfile. Patch is safe: no `sem-core` public API changes since v0.16.0
(only an internal `parser/context.rs` fix). Merging this triggers the
release workflow, which cuts v0.16.1 and publishes the first registry
entry.

## Verification done

- `server.json` validated against the official registry JSON schema
(ajv)
- npm wrapper tests pass; `sync-package-version.mjs` preserves `mcpName`
- jq stamp command tested locally; workflow YAML parses
- `mcp-publisher` release asset name
(`mcp-publisher_linux_amd64.tar.gz`) confirmed against the registry's
latest release
- Registry API confirmed no existing `io.github.ataraxy-labs/*` entries