…orkers can resolve it

#3811 introduced `_simulation-queue-constants.mjs` at `server/_shared/`
and had `scripts/seed-forecasts.mjs` import it via `../server/_shared/...`.
That works in dev and on Vercel (esbuild inlines), but the three Railway
services that run the seeder — `seed-forecasts`, `simulation-worker`,
`deep-forecast-worker` — use the nixpacks build with `root_dir=scripts`,
which packages only `scripts/` contents into `/app/` in the container.

The relative import resolves to `/server/_shared/_simulation-queue-
constants.mjs` at runtime — a path that does not exist in the container —
and crashes every worker on startup:

  Error [ERR_MODULE_NOT_FOUND]: Cannot find module
  '/server/_shared/_simulation-queue-constants.mjs'
  imported from /app/seed-forecasts.mjs

All three Railway services have been in a crash loop since #3811 merged.

Fix: move the shim into `scripts/` (where it ships alongside the seeder)
and update the 4 importers:

  - scripts/seed-forecasts.mjs          → './_simulation-queue-constants.mjs'
  - server/_shared/simulation-queue.ts  → '../../scripts/_simulation-queue-constants.mjs'
  - server/worldmonitor/forecast/v1/trigger-simulation.ts    → '../../../../scripts/...'
  - server/worldmonitor/forecast/v1/get-simulation-outcome.ts → '../../../../scripts/...'

esbuild bundles the shim inline at Vercel build time, so the cross-
directory `../../scripts/...` path is fine on the server side. The
`.d.mts` declaration moves alongside so TS module-resolution still
picks it up. The shim's own header now documents WHY it lives in
scripts/ to prevent the next contributor from "tidying" it back into
server/_shared/.

Regression test: tests/scripts-railway-nixpacks-no-escape-import.test.mts.
BFS-walks `scripts/seed-forecasts.mjs`, `scripts/process-simulation-tasks.mjs`,
and `scripts/process-deep-forecast-tasks.mjs` (the three Railway service
entry points), following every relative import inside `scripts/`, and
fails if any resolved path escapes `scripts/`. Verified that the test
correctly fails with the broken import restored, then passes after fix.

Verification:
  - typecheck (main + api): clean
  - simulation tests: 30/30 pass (27 existing + 3 new)
  - docker/build-handlers.mjs: completes with 0 failures
  - shim resolves at runtime from both old (.mjs entry) and esbuild path

Distinct from #3811's Vercel-Edge fix commit (Web Crypto port) — that
addressed a build-time bundler error; this addresses a runtime
container-packaging error that only fires on Railway. No tests in #3811
exercised a Railway-shipped resolution path, which is how this escaped
review. The new test closes that coverage gap for these three workers
and any future scripts/ entry added to ENTRY_POINTS.

1. Shim header missing the Railway-packaging rationale (P2).
   Three importers (server/_shared/simulation-queue.ts and the two
   forecast/v1 handlers) added "see the header of
   scripts/_simulation-queue-constants.mjs for the Railway packaging
   reason" cross-references in their import comments, but the shim
   itself was renamed with similarity index 100% — its header was
   the original Edge-bundling note with no mention of why it lives
   in scripts/ now. My header edit was made locally but never staged
   before the previous commit, so the published file shipped without
   the rationale. Fix: rewrite the header to lead with "DO NOT MOVE
   THIS FILE BACK TO server/_shared/", spell out the nixpacks
   root_dir=scripts mechanism, name the three affected Railway
   services, and link the regression test + incident PRs. A future
   contributor opening the shim to "tidy" it will now find an
   in-file warning instead of needing to chase importer comments.

2. isBareOrNode dead code in the BFS loop (P2).
   collectRelativeImports already pre-filters to `./` and `../`
   specs only, so isBareOrNode(spec) in the loop body always
   returned false and the `continue` was never reached. Removed
   both the unused helper and the loop guard.

Tests still 3/3 pass; typecheck:api clean.