kernel: align VERSION with the beta target (0.0.1.dev0) and document the versioning scheme

[JArmandoAnaya]

Context

VERSION currently reads 0.1.0.dev0, but the roadmap target is 0.0.1-beta, which is
lower in semver. Nothing has been published, so this is a one-line fix — but it blocks
tagging any v0.0.1-alpha.N.

Deliverables

• VERSION → 0.0.1.dev0.
• CONTRIBUTING section documenting the scheme: internal milestone tags v0.0.1-alpha.N
  (git tags only, never published), beta = 0.0.1b1 on PyPI (PEP 440) /
  0.0.1-beta.1 on npm, lockstep across the monorepo.
• Verify uv run visionset --version and the npm version-sync script both pick it up.

Acceptance criteria

• uv run visionset --version prints 0.0.1.dev0
• npm workspace packages report the synced version
• CONTRIBUTING documents the tag/publish scheme

[JArmandoAnaya]

Done: VERSION → 0.0.1.dev0, frontend packages resynced to 0.0.1-dev.0, openapi.json regenerated, and CONTRIBUTING now carries the full PEP 440 ↔ npm table plus the tag-vs-publish scheme. PR #71.
Decisions: (1) Generalized scripts/sync_versions.mjs to map a/b/rc as well as .devN — the documented 0.0.1b1 → 0.0.1-beta.1 mapping would otherwise have written an invalid npm version; unmappable versions now throw. (2) Added pnpm version:check as a CI drift gate, since "npm packages report the synced version" is only durable if something enforces it. (3) The mapping is unit-tested with the built-in node:test runner (pnpm test:scripts, folded into pnpm test) — scripts/ sits outside the pnpm workspace, so vitest had no natural home there.
Follow-ups: none — openapi.json drifting on every VERSION bump is already covered by the existing OpenAPI drift gate, which caught it here.
Next: #10 — kernel: bbox/polygon geometry as a pydantic discriminated union (per the M1 sequence).