[CI] Clean up formatting and promote format checks to required

[Darkroom4364]

Follow-up from #85 CI setup.

Current state:

• gofmt -l server reports existing formatting drift in several Go files.
• cargo fmt --check reports broad Rust formatting drift in the agent.
• The new CI workflow includes formatting as an advisory job so build/test gates can start immediately without making the initial workflow red.

Acceptance criteria:

• Run gofmt on server Go files and cargo fmt on the agent.
• Review the mechanical diff for accidental churn.
• Change the CI format job from advisory to required by removing continue-on-error: true.
• Confirm go test ./... in server/ and cargo test --locked in agent/ still pass.

[Darkroom4364]

Closing as completed by PR #91, merged into dev. Post-merge dev CI is running under https://github.com/Darkroom4364/MicroC2/actions/runs/26722527587.