Move from npm to pnpm across the workspace, CI and the image

The monorepo was on npm workspaces. pnpm gives it a content-addressed store
shared between the eight packages, a lockfile that records the whole graph
rather than a flattened view of it, and — the reason this mattered in practice —
`workspace:*`, which makes an internal dependency unambiguous instead of a
version range that npm may satisfy from the registry.

Mechanics:

  - `packageManager: pnpm@11.21.0` pins the version; corepack installs it in CI
    and in the image, so all three environments resolve identically.
  - The npm `workspaces` array is replaced by `pnpm-workspace.yaml`. pnpm
    ignores the former, and keeping both would leave two sources of truth.
  - All six internal dependencies moved to `workspace:*`.
  - Root scripts use `pnpm -r --if-present` and `pnpm -F <pkg>`.

Two findings worth recording, both from running it rather than reading it:

`tsx` was a devDependency, but the server runs TypeScript directly in
production — the container's command is `pnpm exec tsx apps/api/src/server.ts`.
Under npm this was concealed by the runtime stage re-installing tsx by hand
after pruning dev dependencies. Under `pnpm install --prod` that sleight of
hand stops working and the image simply fails to start. tsx is now declared in
`dependencies`, which is what it has always actually been.

The first image build failed with ERR_PNPM_ABORTED_REMOVE_MODULES_DIR_NO_TTY.
That is not a pnpm bug: it had decided the modules directory was stale and
wanted confirmation before deleting it, which a non-interactive build cannot
give. The trigger was the host's `node_modules` reaching the build context —
there was no `.dockerignore` at all. pnpm's tree is symlinks into a
content-addressed store, so copying it into an image produces dangling links
and a directory pnpm rightly considers corrupt. Fixed by adding
`.dockerignore` and setting `CI=true`, which is required in any non-interactive
pnpm build.

`esbuild` is denied install scripts via `allowBuilds`. Its platform binary
arrives through the optional dependency `@esbuild/linux-x64` and the postinstall
only verifies it; confirmed by running the binary directly, which reports
0.25.12.

Verified under pnpm: typecheck clean, 150 tests / 0 failures, e2e passes, web
builds. The image was built and booted against a real Postgres — health ok,
`/api/dashboard` 401 with an issuer configured, `/` and `/capacity` serve the
SPA, `/og.png` serves as image/png, and the migrator runs from the pruned
runtime stage.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/seed-data.md

@@ -47,7 +47,7 @@ permanently.
 Seeding is a separate command and is never automatic:
 
 ```bash
-npm run db:seed     # opt in
+pnpm run db:seed     # opt in
 ```
 
 Skip it and PIG starts empty apart from a development user.