#133 chore: organise the repository layout

Tidies the repository layout without touching code or the root's standard files (README, LICENSE, Makefile, Dockerfile, docker-compose.yml, go.mod and the community files all stay).

• AetherCode.png, Architecture.png moved to docs/assets/.
• deploy/aethercode-exec.service and deploy/env.example moved to deploy/systemd/; deploy/alerts.yml to deploy/monitoring/.
• docs/benchmark-results.md and docs/spike-results.md moved to docs/benchmarks/.
• code-rabbit.yml removed: CodeRabbit reads .coderabbit.yaml, which stays, so the older file did nothing.
• README gains a "Repository layout" table; every reference to a moved file (README, ARCHITECTURE, CHANGELOG, .goreleaser.yml, the docker-compose.yml comment) is updated.

Testing

go build ./... and go vet ./... clean. No Go code changed; nothing in .github/workflows referenced a moved path.

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Summary by cubic

Reorganises the repository layout to group related files, with no Go code changes.

• Moves deploy files into deploy/systemd/ and deploy/monitoring/, images into docs/assets/, and benchmark/spike results into docs/benchmarks/.
• Removes code-rabbit.yml, which was doing nothing since .coderabbit.yaml is the config CodeRabbit reads.
• Updates every reference to the moved files (README, ARCHITECTURE, CHANGELOG, .goreleaser.yml, docker-compose.yml) and adds a "Repository layout" table to the README.