feat(artifacts): add slim field-projected search-index artifact

[andriypolanski]

Summary

Adds search-index.json — a token-stripped projection of search.json — and
the corresponding /api/v1/search-index route. The slim index carries the same
document count and IDs as the full index but omits per-document token blobs,
making it significantly lighter for browser typeahead and listing use-cases.
Served from R2 only (never committed as a static artifact).

What Changed

• schemas/api-components.schema.json + schemas/components/08-evidence-search-sources.schema.json +
  schemas/public-artifacts.schema.json: new SearchIndexArtifact /
  SearchIndexDocument schemas
• src/artifact-storage.mjs: R2-only tier entry for search-index.json
• src/contracts.mjs: artifact and /api/v1/search-index route registration
• scripts/build-artifacts.mjs: buildSlimSearchIndex writes search-index.json
  alongside (not instead of) search.json
• scripts/validate-api.mjs: live-API check for the new route
• tests/artifacts.test.mjs: lock-step consistency assertions — same count, same
  IDs, no token blobs, field-for-field equality minus tokens
• tests/api-coverage.test.mjs: slim route serve test + field-projection test
• generated/ + public/metagraph/: regenerated OpenAPI, types, api-index, and
  contracts via npm run build on current main
• packages/client/package.json + package-lock.json: version bumped
  0.7.0 → 0.8.0 (new route added to the published contract)
• docs/backend-artifact-contracts.md: contract documentation update

Registry Safety

• No secrets, PATs, wallet data, private dashboards, private URLs, or
  validator-local state.
• Generated artifacts were produced by npm run build on current main.
• R2-only/high-churn detail artifacts are not committed.
• Public API/OpenAPI/schema changes are intentional and documented.

Validation

• git diff --check
• npm run build (all steps green)
• npm run validate
• npm run validate:schemas
• npm run validate:api
• npm run validate:openapi
• npm run scan:public-safety

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.23%. Comparing base (2bcd5c1) to head (4464ab3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1975   +/-   ##
=======================================
  Coverage   93.23%   93.23%           
=======================================
  Files          48       48           
  Lines        7626     7626           
  Branches     2804     2804           
=======================================
  Hits         7110     7110           
  Misses         90       90           
  Partials      426      426           

Files with missing lines	Coverage Δ
src/artifact-storage.mjs	100.00% <ø> (ø)
src/contracts.mjs	94.31% <ø> (ø)

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[andriypolanski]

Hi, @JSONbored
I’m trying to fix a CI error that occurred during testing, but I haven’t been able to resolve it yet. Could you please help me take a look?

[JSONbored]

Merging. I closed #1889 for bundling the scripts/lib.mjs Windows path fix alongside this — I asked you to split them. This is the correctly split version: no lib.mjs changes in the diff, just the slim search-index artifact. Removes the per-document tokens blobs (~1.1 MB saved) that typeahead and list rendering never use. All generated artifacts regen'd, client bumped 0.9.0 → 0.10.0. Green CI.