fix: mark @orpc packages as sideEffect-free for cross-pkg tree-shaking (#1540)

Closes #1490.

## Background

Importing only `oz.file()` from `@orpc/zod` was pulling ~21 kB of
`@orpc/server` runtime into client bundles via the chain:

```
@orpc/zod  →  @orpc/openapi  →  @orpc/server
```

Because `@orpc/zod` re-exports `JSONSchemaFormat` etc. from
`@orpc/openapi`, and `@orpc/openapi/dist/index.mjs` has top-level
`import { ORPCError, createRouterClient } from '@orpc/server'`. Those
top-level cross-package imports are preserved by the consumer's bundler
unless the package is annotated as side-effect free, because the bundler
cannot otherwise prove the import has no observable effect.

## Fix

Add `"sideEffects": false` to the all oRPC's packages

I audited the source for global mutations / prototype patches /
side-effecting class registrations at import time and found none — the
published modules are pure, so the annotation is safe.

## Reproducer

Stand-alone Vite app that mirrors the issue body:

```ts
// client.ts
import { oc } from '@orpc/contract'
import { z } from 'zod/v3'
import { oz } from '@orpc/zod'

export const myRouter = oc.router({
  downloadFile: oc
    .route({ method: 'GET', path: '/download/{id}' })
    .input(z.object({ id: z.string() }))
    .output(oz.file()),
})
```

Bundled with `vite build --minify esbuild --target es2022` and
`external: ['zod', 'zod/v3']`:

| Variant | Bundle | Gzipped | `@orpc/server` symbols leaked |
|---|---|---|---|
| Before this PR | **37.9 kB** | 9.54 kB | `ORPCError`, `Procedure`,
`createRouterClient`, `isProcedure`, `resolveContractProcedures` |
| After this PR | **14.8 kB** | 4.76 kB | none from `@orpc/server` (the
remaining `ORPCError` is from `@orpc/contract`, which is legitimately
needed because `oc.router()` returns objects that use it) |

**Net savings: 23.1 kB minified (61% reduction) / 4.78 kB gzipped
(50%).**

## Why this rather than the subpath split suggested in #1490

The reporter (correctly) suggested splitting `ZodToJsonSchemaConverter`
into a separate `@orpc/zod/json-schema` subpath and removing it from the
main entry. That would also fix the bug, but it is a **breaking change**
for everyone currently importing the converter from `@orpc/zod` (incl.
all in-repo playgrounds that use `@orpc/zod/zod4`'s sister export,
README example, etc.) and the subpath split is bundler-independent only
insofar as users don't accidentally re-export the heavy entry
transitively.

`sideEffects: false` is **non-breaking**, lands in 6 lines, and — as the
numbers show — actually achieves the bundle reduction the reporter
expected. If the cross-package tree-shaking turns out insufficient for
some consumer's bundler, the subpath split is still available as a
follow-up.

The reporter's original claim that `sideEffects: false` alone wouldn't
fix this assumed it was set on `@orpc/zod` only; the chain only
tree-shakes when **every** package along the cross-package import path
is marked, which is what this PR does.

## Local gates

- `pnpm --filter='./packages/*' run -r build` ✓ all packages build, dist
outputs unchanged in shape (sideEffects flag does not alter the
rolled-up bundle, only the `package.json` of the published artifact)
- `pnpm test` ✓ 4720 pass / 48 skipped / 5 todo across 280 test files
(untouched by this change)
- `pnpm run type:check` ✓ clean across all packages
- `pnpm lint` ✓ clean (auto-formatter sorted the new key after
`keywords` per `jsonc/sort-keys`)

I was happy to find this fits in 6 lines — happy to fold in the subpath
split as a follow-up if any reviewer measures their bundler still needs
it.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Chores**
* Updated package metadata across many packages to mark them as
side-effect free for improved bundling behavior.
* **New Features**
* Exposed a package entry point for one package, updating its public
exports.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: voidborne-d <258577966+voidborne-d@users.noreply.github.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Co-authored-by: Dinh Le <dinwwwh@gmail.com>

Author: 3 people

packages/ai-sdk/package.json

@@ -13,6 +13,7 @@
     "ai-sdk",
     "orpc"
   ],
+  "sideEffects": false,
   "publishConfig": {
     "exports": {
       ".": {

packages/arktype/package.json

@@ -12,6 +12,7 @@
   "keywords": [
     "orpc"
   ],
+  "sideEffects": false,
   "publishConfig": {
     "exports": {
       ".": {

packages/client/package.json

@@ -12,6 +12,7 @@
   "keywords": [
     "orpc"
   ],
+  "sideEffects": false,
   "publishConfig": {
     "exports": {
       ".": {

packages/contract/package.json

@@ -12,6 +12,7 @@
   "keywords": [
     "orpc"
   ],
+  "sideEffects": false,
   "publishConfig": {
     "exports": {
       ".": {

packages/durable-iterator/package.json

@@ -12,6 +12,7 @@
   "keywords": [
     "orpc"
   ],
+  "sideEffects": false,
   "publishConfig": {
     "exports": {
       ".": {

packages/hey-api/package.json

@@ -13,6 +13,7 @@
     "orpc",
     "Hey API"
   ],
+  "sideEffects": false,
   "publishConfig": {
     "exports": {
       ".": {

packages/interop/package.json

@@ -12,6 +12,7 @@
   "keywords": [
     "orpc"
   ],
+  "sideEffects": false,
   "publishConfig": {
     "exports": {
       "./compression": {

packages/json-schema/package.json

@@ -12,6 +12,7 @@
   "keywords": [
     "orpc"
   ],
+  "sideEffects": false,
   "publishConfig": {
     "exports": {
       ".": {

packages/nest/package.json

@@ -12,6 +12,7 @@
   "keywords": [
     "orpc"
   ],
+  "sideEffects": false,
   "publishConfig": {
     "exports": {
       ".": {

packages/openapi-client/package.json

@@ -12,6 +12,7 @@
   "keywords": [
     "orpc"
   ],
+  "sideEffects": false,
   "publishConfig": {
     "exports": {
       ".": {