outboundByHost / interceptHttps breaks when worker uses placement: targeted

**Describe the bug**

When a Cloudflare Worker using `@cloudflare/sandbox` has `placement: { mode: "targeted", region: "..." }` set in `wrangler.jsonc`, the `outboundByHost` handler is never invoked for HTTPS traffic originating inside the container. Switching to `placement: { mode: "smart" }` (or removing the placement block entirely) fixes interception with no other code changes.

**To Reproduce**

1. Create a Sandbox subclass with `interceptHttps = true` and a static `outboundByHost` handler:

```ts
export class MySandbox extends Sandbox {
interceptHttps = true
defaultPort = 3000
}

MySandbox.outboundByHost = {
'api.anthropic.com': () =>
new Response('intercepted', {
status: 200,
headers: { 'x-test-intercepted': 'yes', 'content-type': 'text/plain' },
}),
}
```

2. Add `"placement": { "mode": "targeted", "region": "aws:eu-west-2" }` to `wrangler.jsonc`.
3. Deploy and run `sandbox.exec('curl -sS -i --max-time 5 https://api.anthropic.com/')` from a worker handler.
4. Observe: `x-test-intercepted` header is absent from the curl output (outbound bypasses the handler entirely).
5. Remove the `placement` block (or change to `"mode": "smart"`), redeploy.
6. Observe: `x-test-intercepted: yes` is present — handler fires correctly.

**Expected behavior**

`outboundByHost` handlers should intercept container outbound HTTPS traffic regardless of the worker's placement mode.

**Screenshots**

With `placement: { mode: "smart" }` — interception works. The `Cf-Placement` response header shows the worker and container running in the same colo (`local-CDG`):
```json
{ "intercepted": true, "stdoutHead": "HTTP/1.1 200 OK\r\nCf-Placement: local-CDG\r\n...X-Test-Intercepted: yes\r\n\r\nintercepted" }
```

With `placement: { mode: "targeted", region: "aws:eu-west-2" }` — handler never fires:
```json
{ "intercepted": false, "stdoutHead": "" }
```

**Version**

- `@cloudflare/sandbox`: 0.9.2
- `@cloudflare/containers`: 0.3.3
- Wrangler: 4.84.0
- `compatibility_date`: 2026-04-22
- `compatibility_flags`: `["nodejs_compat"]`

**Additional context**

The `Cf-Placement: local-CDG` header in the working case suggests that targeted placement pins the entry worker to a different colo from where the container and its `ContainerProxy` isolate run. The SDK's handler registry (`outboundByHostRegistry`) is per-isolate, so the `ContainerProxy` isolate in the container's colo never sees the handler registered by the entry worker's isolate.

Workaround: use `placement: { mode: "smart" }` instead of `targeted`.