fix(#21): lexicon root re-exports + silent build-failure guard + composite spread

[lex00]

Summary

Closes #21. Three bugs were called out in that issue, plus one I tripped over while verifying the fix end-to-end.

• gcp/k8s lexicon root indexes were missing re-exports for MultiRegionVpc, GkeCrdbRegion, CockroachDbRegionStack (and their config types) — they were exported from each lexicon's composites/index.ts but not surfaced at the package root, so import { MultiRegionVpc } from "@intentius/chant-lexicon-gcp" failed on a fresh npm install. Existing dev machines hid the gap because node_modules/@intentius/chant-lexicon-* was a symlink into source.
• chant build silent-success-with-empty-output (the secondary bug in lexicon root index.ts misses three composites — chant build fails silently when examples import them #21): when imports resolved to undefined without being invoked, discovery completed with zero declarables, chant wrote "{}" to the output file and exited 0. First sign of trouble was kubectl apply failing at deploy time. Now: when sourceFileCount > 0 but outputs.size === 0, surface a descriptive error and skip the file write.
• Composite spread footgun (new): spreading a composite instance (...someComposite) leaked the framework's bookkeeping (members, _definition) into the receiving object. A parent composite that did ...childResult then tripped its own member validation with "is not a Declarable or CompositeInstance". Made members/_definition non-enumerable so spread only exposes actual member resources.
• Example cleanup: temporal-crdb-deploy had per-region export const cluster = east.cluster re-exports that duplicated the same Declarables under names that collided when chant scanned the full src/ tree (e.g. for build:temporal). Composite expansion already produces uniquely-prefixed names, so the re-exports were redundant.

Verification

• All 1377 core tests pass.
• Reproduced and confirmed fixed: silent-exit-0 path with a probe file importing a non-existent symbol — now exits 1 with a clear message and no out.yaml written.
• Before/after probe inside examples/temporal-crdb-deploy: 10 TS2305 missing-export errors → 0 after the lexicon fix.
• Built examples/temporal-crdb-deploy end-to-end: all 8 dist artifacts produced (temporal-setup.sh, shared-infra.yaml, {east,central,west}-{infra,k8s}.yaml).

Version bumps

• @intentius/chant 0.1.6 → 0.1.7 (silent-build-failure guard, composite spread fix)
• @intentius/chant-lexicon-gcp 0.1.5 → 0.1.6 (root re-exports)
• @intentius/chant-lexicon-k8s 0.1.5 → 0.1.6 (root re-export)

Release plan

Once this is merged, push these three tags from main to trigger the publish workflows:

git tag chant-v0.1.7
git tag lexicon-gcp-v0.1.6
git tag lexicon-k8s-v0.1.6
git push origin chant-v0.1.7 lexicon-gcp-v0.1.6 lexicon-k8s-v0.1.6

After publish, a fresh cd examples/temporal-crdb-deploy && npm install && npm run build will pick up the new versions and build cleanly.

Test plan

• CI: npx vitest run passes (1377 tests in core).
• CI: npm run build per touched lexicon prepack (covered by the existing test job in .github/workflows/publish.yml).
• Manual: with workspace symlinks, cd examples/temporal-crdb-deploy && npm run build produces 8 dist artifacts with no errors.
• Manual: probe file with a missing import and no invocation — chant build exits 1, no output file written.