[deep-report] Remove stray compiled binary test_dup_import from repo root

### Description
A 2.3MB compiled Go binary, `test_dup_import` (ELF 64-bit, statically linked, unstripped), is checked into the repository root and tracked in git. It was flagged by the 2026-09-15 UK AI Resilience weekly review as a commit-hygiene gap alongside a secret-validation PR — compiled artifacts shouldn't be committed to `main`.

### Expected Impact
Removes a stray 2.3MB binary from repo history going forward, prevents repo bloat, and closes an automation commit-hygiene gap (a build output landed in a commit instead of being gitignored).

### Suggested Fix
Delete `test_dup_import` from the working tree and add a `.gitignore` entry (or equivalent pattern) so future builds of this test artifact aren't accidentally committed again.

### Suggested Agent
New Agent (small cleanup PR) or code-simplifier

### Estimated Effort
Quick (< 30 min)

### Data Source
DeepReport Intelligence Briefing analysis, 2026-09-15 cycle 3 — derived from [uk-ai-resilience] Weekly recent-change risk & resilience review (#61164)

> [!WARNING]
>
> Firewall blocked 1 domain
>
> The following domain was blocked by the firewall during workflow execution:
>
> - `api.anthropic.com`
>
> To allow these domains, add them to the `network.allowed` list in your workflow frontmatter:
>
> ```yaml
> network:
> allowed:
> - defaults
> - "api.anthropic.com"
> ```
>
> See [Network Configuration](https://github.github.com/gh-aw/reference/network/) for more information.
>
>

> Generated by [🔬 Deep Report](https://github.com/github/gh-aw/actions/runs/35007359021) · claude · agent · 221.8 AIC · ⌖ 11.2 AIC · ⊞ 12.8K · [◷](https://github.com/search?q=repo%3Agithub%2Fgh-aw+is%3Aissue+%22gh-aw-workflow-call-id%3A+github%2Fgh-aw%2Fdeep-report%22&type=issues)
> - [x] expires on Sep 17, 2026, 10:41 AM UTC-08:00

Start at the repository root by confirming the tracked `test_dup_import` artifact and reviewing the existing `.gitignore` patterns. Remove the binary and add an appropriate ignore entry for this test artifact, then verify that the binary is no longer tracked and future builds cannot accidentally re-add it.

Written by the indexing model from the issue text.