build(frontend)!: knip drops --production; plain knip stays

The production pass (7ed2ac4e, E32) asked "is this export used by what
ships?". No real hit: its only findings were 37 exports a test imports,
answered with 36 `@internal` JSDoc tags (E34 S2) — test-only exports, not
defects. Since then it has only ever asked for another tag. The tags go
with it (36, no longer read by anything), and so do the production-only
`!…!` exclusions in knip.jsonc and their register rows. Plain knip (unused
files, exports and dependencies) keeps running in the gate.

docs/development.md

@@ -97,7 +97,7 @@ node ../scripts/check-node-modules.mjs   # node_modules == package-lock.json (el
 npm run typecheck     # tsc x3 (app / node / e2e)
 npm run lint          # eslint (typed rules included; warnings fail)
 npm run format:check  # prettier
-npm run knip          # unused files/exports/deps — and unused by what SHIPS (--production)
+npm run knip          # unused files/exports/deps
 npm run test          # vitest (incl. the compiler and gate-register contracts)
 npx vite build        # the production bundle (devOnlyGuard fails it on dev-only code)
 npm audit --omit=dev --audit-level=high   # what ships to the browser, at high or above