docs: correct claims that no longer match the code

[retr0h]

Part of correct-documentation-drift.

• CLAUDE.md described nats-client and nats-server as linked via a replace directive. go.mod has no replace; both are pinned module versions.
• CLAUDE.md named printKV and printStyledTable in cmd/ui.go. Neither symbol nor that file exists — the helpers are cli.PrintKV and cli.PrintCompactTable in internal/cli/ui.go.
• system-architecture.md located the notifier at internal/notify/; it is internal/controller/notify/.
• configuration.md said two fields carry a required tag. Seven do — five have viper.SetDefault() values, so only two must be set. Its table also carried two controller.metrics rows pasted from the environment-variable table above it.
• intro.md prefixed four links with sidebar/ while already inside sidebar/, and linked category/api without the leading slash the other five references use.

just md-fmt-check and just docusaurus-fmt-check clean.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@           Coverage Diff           @@
##             main     #445   +/-   ##
=======================================
  Coverage   99.94%   99.94%           
=======================================
  Files         484      484           
  Lines       24935    24935           
=======================================
  Hits        24921    24921           
  Misses         14       14           

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