chore(cleanup): delete 16 dead helper+test pairs (~7,400 LOC)

Per the new deadcode-removal scan's shape-2 (test-only helpers): each
of these src files has zero non-test importers anywhere in the
monorepo. The only consumer of every export was the colocated
.test.mts. Per the scan's rule — when the only consumer IS the test,
delete both the helper AND its test together; preserving either is
circular.

Deleted pairs (src LOC + test LOC):
  util/socket/package-alert.mts        (648 + 1546)  15 unused exports
  util/project/context.mts             (255 +  639)   6 unused exports
  util/npm/spec.mts                    (193 +  485)   4 unused exports
  util/validation/ipc.mts              (142 +  366)   6 unused exports
  util/cli/messages.mts                (151 +  353)  12 unused exports
  util/command/logger.mts              (203 +  245)   6 unused exports
  util/coana/spawn.mts                 (132 +  194)   1 unused export
  util/promise/queue.mts               (140 +  158)   1 unused export
  util/npm/config.mts                  ( 69 +  182)   1 unused export
  util/pnpm/paths.mts                  ( 51 +  187)   3 unused exports
  yarn-cli.mts                         ( 37 +  169)   1 unused export
  npm-cli.mts                          ( 37 +  166)   1 unused export
  pnpm-cli.mts                         ( 37 +  166)   1 unused export
  npx-cli.mts                          ( 36 +  163)   1 unused export
  util/home-cache-time.mts             ( 31 +  163)   1 unused export
  util/output/adapters/index.mts       ( 29 +   43)   1 unused export

Notes on the *-cli.mts entry points: package.json `bin` declares
only `socket`, `socket-npm`, `socket-npx` all pointing at
dist/index.js (which dispatches based on argv[0]). The `npm-cli.mts`
etc. files have self-invocation entry shims (`if import.meta.url ===
argv[1]`) but nothing references their file paths from the build
config, the package.json bin field, or runtime — they're orphaned
entry shims from an earlier dispatch design. The new
`socket-npm`/`socket-npx` flow goes through cli-dispatch.mts.

Verification:
  - `tsc --noEmit` passes
  - `pnpm exec oxlint --config .config/oxlintrc.json .` passes

Author: jdalton