feat(mapping): centralize domain <-> contracts mappings (B5)

New @umt/mapping (depends on domain + contracts only): download status + pause reason,
evidence level / media kind, identity resolution status, slot status / spec columns /
evaluation, ParsedRelease <-> source_release.parsed, SiteRelease <-> source_release,
PathBinding, OrganizePlan -> organization_record / file results / organize.plan output.
Tables are Record<union, ...> so adding a value on either side fails typecheck or tests.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/mapping/deno.json

@@ -0,0 +1,9 @@
+{
+  "name": "@umt/mapping",
+  "version": "0.0.0",
+  "exports": { ".": "./src/index.ts" },
+  "tasks": {
+    "test": "deno run -A npm:vitest run",
+    "typecheck": "deno run -A npm:typescript/tsc --noEmit -p tsconfig.json"
+  }
+}