Add deterministic Core primitives for issue #2

[knqiufan]

Summary

• Ship @powercontext/core JCS, NFC, domain hash, refs, UTF-8 budgets, and fake-store revision/head traces for the sqlite-fts / C2 profile.
• Keep IEEE floats such as 1e30 on the domain path, reject unsafe Python-int tokens before parse, and hash identity values through hashDomain.
• Validate Artifact lineage refs, make Source fake-store identity idempotent, implement ArtifactCatalog on the fake store, and project typed refs to snake-case wire JSON.
• Move shared canonical fixtures through the Core package and keep Python rfc8785 as the oracle.
• Record the IEEE versus Python-int split in ADR 0006.

Test plan

• pnpm exec vitest run packages/core (114 passed)
• pnpm exec vitest run packages/conformance-runner (10 passed)
• Confirm C2 canonical fixtures still match conformance/expected/canonical.json, including domain.float-1e30
• Read ADR 0006 and confirm the IEEE / Python-int split is explicit

Closes #2