refactor(cli): delete internal barrel index.ts files

The 34 `index.ts` re-export barrels inside `packages/cli/src/` were
holdovers from the pre-fold multi-workspace structure. Post-fold-in they
served no production purpose: external consumers go through the single
package main entry, and in-repo callers mostly imported through them
only because the path was short. Internally, knip flagged most barrel
re-exports as production-dead (only reached via tests).

This change:
- Deletes every internal barrel except `packages/cli/src/index.ts`
  (the published package entry).
- Rewrites ~270 source/test files to import each name directly from
  the file that defines it.
- Moves `tools/warehouse-verification/index.ts` to
  `create-warehouse-verification-tools.ts` (the function it defined
  locally) and updates its single consumer.
- Renames `search/backend-conformance.ts` → `.test-utils.ts` to match
  the existing test-helper file convention.
- Deletes 13 dead test-only chains (dbt-descriptions/*,
  live-database/extracted-schema, live-database/structural-sync,
  relationship-* feedback/review chain) plus their tests and a
  cascading orphan integration test.
- Updates test mocks that pointed at deleted barrel paths
  (notion-client, connector barrels in scan/local-scan-connectors
  tests) to mock the source files instead.
- Points the maintainer benchmark script
  (`scripts/relationship-benchmark-report.mjs`) at source files
  instead of `dist/context/scan/index.js`.
- Drops the barrel `!` entries from `knip.json`; adds explicit
  production entries only for the benchmark code reached via dist by
  the maintainer script.

Net: 413 files changed, ~1.2k insertions, ~9.4k deletions.

`pnpm run dead-code` (Biome + knip default + knip production) and
`pnpm run type-check` are clean; 2277 tests pass.

scripts/relationship-benchmark-report.mjs

@@ -1,14 +1,16 @@
 import { dirname, join, resolve } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import {
-  KTX_RELATIONSHIP_BENCHMARK_MODES,
   buildKtxRelationshipBenchmarkReport,
-  currentKtxRelationshipBenchmarkDetector,
   formatKtxRelationshipBenchmarkReportMarkdown,
+} from '../packages/cli/dist/context/scan/relationship-benchmark-report.js';
+import {
+  KTX_RELATIONSHIP_BENCHMARK_MODES,
+  currentKtxRelationshipBenchmarkDetector,
   ktxRelationshipBenchmarkDetectorWithLlm,
   loadKtxRelationshipBenchmarkFixtures,
   runKtxRelationshipBenchmarkSuite,
-} from '../packages/cli/dist/context/scan/index.js';
+} from '../packages/cli/dist/context/scan/relationship-benchmarks.js';
 
 const scriptDir = dirname(fileURLToPath(import.meta.url));
 const ktxRoot = resolve(scriptDir, '..');