v0.12.1 — unified binary (setup wizard as subcommand)

Highlights

• One binary per platform instead of two (#487) — the setup wizard is now invoked as a subcommand, vaultpilot-mcp setup. The MCP server and setup wizard ship as a single vaultpilot-mcp-<platform>-<arch>-server binary; the standalone *-setup binaries are gone. Halves bandwidth per release (~2.4 GB → ~1.2 GB) and eliminates the macos-x64-setup flake leg that was the most frequent post-release blocker on v0.12.0.

Backward compat

• Binary path: the *-server asset name is preserved. Users following the latest install.sh / install.ps1 get the unified binary at the same URL automatically.
• npm path: the vaultpilot-mcp-setup bin entry still works — it's a backward-compat shim that points at dist/setup.js directly. Both vaultpilot-mcp setup and vaultpilot-mcp-setup are valid on npm.

Included PRs

• #487 feat(release): unify server + setup wizard into one binary via setup subcommand
• #488 chore(release): bump to 0.12.1

Deliberately deferred

• Cross-OS validation in CI separate from the release run. This release IS the first cross-OS test of the unified-binary code; release-binaries.yml is the integration harness. If the macos-x64 leg flakes, that's a runner issue, not the new code (the argv-detection contract is unit-tested at 7 cases).