#405 docs: add performance documentation and update repository hygiene

Description

## Intent

Repository hygiene + documentation for the 2026-10-01 ROCm/gfx1100 perf work: extend .gitignore (bench-*.json, *.bak, *.orig, *.tuned, .lavish/); track OPTIMISATION.md, docs/perf-notes/, opencode-perf-prompt.md, bench/results/2026-09-30-nixos-mmq-ring96-ple0, voxel-world/, sermon-on-the-mount.html. Docs-only change; test/document/lint skipped (no runtime behavior; agent instability on IQ1_M). Fork-based PR flow now configured: push to jase100k/Strata fork, PR against Niko1221/Strata.

## What Changed
- Extended .gitignore to ignore bench-*.json, *.bak, *.orig, *.tuned, .lavish/
- Added performance optimization documentation (OPTIMISATION.md, opencode-perf-prompt.md, docs/perf-notes/)
- Added benchmark results and trials for ROCm/gfx1100 performance run on 2026-09-30, plus example files (sermon-on-the-mount.html, voxel-world/index.html)

## Risk Assessment

⚠️ Medium: The change adds interactive 3D applications that contradict the user intent of a docs-only change with no runtime behavior, creating a mismatch between expected and actual behavior.

## Testing

- ⏭️ **Test** - skipped

## Pipeline

Updates from [git push no-mistakes](https://github.com/kunchenguid/no-mistakes)

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<details>
<summary>✅ **intent** - passed</summary>

✅ No issues found.
</details>

<details>
<summary>✅ **Rebase** - passed</summary>

✅ No issues found.
</details>

<details>
<summary>⚠️ **Review** - 1 warning</summary>

- ⚠️ `sermon-on-the-mount.html:1` - The change adds interactive 3D voxel world applications (sermon-on-the-mount.html and voxel-world/index.html) which have runtime behavior, contradicting the user intent of a &#39;Docs-only change&#39; with &#39;no runtime behavior&#39;.
</details>

<details>
<summary>⏭️ **Test** - skipped</summary>

Step was skipped.
</details>

<details>
<summary>⏭️ **Document** - skipped</summary>

Step was skipped.
</details>

<details>
<summary>⏭️ **Lint** - skipped</summary>

Step was skipped.
</details>

<details>
<summary>✅ **Push** - passed</summary>

✅ No issues found.
</details>