Add DDoS mitigation reasons section to Spectrum documentation

[anita-tenjarla]

Summary

The existing documentation in ddos-protection/advanced-ddos-systems/concepts contains mitigation reason explanations for Advanced DDoS Protection. Add similar documentation for Spectrum.

Documentation checklist

• The change adheres to the documentation style guide.
  =

[cloudflare-docs-bot]

Review

💡 1 suggestion found in commit 30cae80.

Fix in your agent

Fix the following review findings in PR #32077 (https://github.com/cloudflare/cloudflare-docs/pull/32077).

Before making changes, review each finding and present a brief summary table:
- For each finding, state whether you agree, disagree, or need clarification
- If you disagree (e.g. the fix requires disproportionate effort for minimal benefit,
  or the finding is factually incorrect), explain why
- If you need clarification before deciding, ask those questions
- Then share your plan for which issues to tackle and in what order

After triaging, fix all legitimate findings. For any you decide to skip,
post a comment on this PR with the finding ID and your reasoning.

---

## Style Guide Review

### Suggestions (1)

#### SG-85e995001737 · Passive voice
- **File:** `src/content/docs/spectrum/about/ddos-for-spectrum.mdx` line 28
- **Issue:** Line uses passive voice: 'a given packet was dropped by the Spectrum system.'
- **Fix:** Rewrite in active voice, e.g., 'the Spectrum system dropped the packet.'

Code Review

This code review is in beta and may not always be helpful — use your judgment.

_{No code review issues found.}

Conventions

_{No convention issues found.}

Style Guide Review

Suggestions (1)

File	Issue
spectrum/about/ddos-for-spectrum.mdx line 28	Passive voice — Line uses passive voice: 'a given packet was dropped by the Spectrum system.' Fix: Rewrite in active voice, e.g., 'the Spectrum system dropped the packet.'

Commands

Only codeowners can run commands. Post a comment with the command to trigger it.

Command	Description
/review	Runs a review now. Incremental if a prior review exists, full if not.
/full-review	Re-reviews the entire PR diff from scratch, ignoring incremental history. Useful after a rebase, when you want a fresh review, or if the bot gets out of sync and reports issues that no longer exist.
/ignore-review-limit	Permanently lifts the 2-review automatic limit for this PR. Future pushes will trigger reviews as normal.
/disable-auto-review	Stops automatic reviews from triggering on future pushes to this PR. Codeowners can still run /review or /full-review manually.

[cjdoucette]

Exact menu placement can change over time, maybe better to just link to NA