docs: use correct term "Server-Sent Events" in guide

[jtr860830]

This PR updates the terminology in docs/guide.md from "Server-Side Events" to the correct term "Server-Sent Events" (SSE).

Changes:

• Rename the section heading from Server-Side Events to Server-Sent Events.
• Update the description text to use “server-sent events” consistently.

This aligns the docs with the standard naming used in the HTML specification and MDN Web Docs, and should make it easier for readers to search for related resources (e.g. “Server-Sent Events”, “SSE”, EventSource).

Checklist

• I have ensured my pull request is not behind the main or master branch of the original repository.
• I have rebased all commits where necessary so that reviewing this pull request can be done without having to merge it first.
• I have written a commit message that passes commitlint linting.
• I have ensured that my code changes pass linting tests.
• I have ensured that my code changes pass unit tests.
• I have described my pull request and the reasons for code changes along with context if necessary.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.90%. Comparing base (0a6afa5) to head (7ca13bf).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1920   +/-   ##
=======================================
  Coverage   99.90%   99.90%           
=======================================
  Files           9        9           
  Lines        2084     2084           
=======================================
  Hits         2082     2082           
  Misses          2        2           

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[yowainwright]

LGTM