feat: slack notifications

[hcopp]

What changed? Why?

This PR adds slack notifications for when PRs are ready for review and when NPM fails to publish.

I have disabled it for dry runs (previously had enabled for testing).

Testing

How has it been tested?

Was tested manually

Testing instructions

Illustrations/Icons Checklist

Required if this PR changes files under packages/illustrations/** or packages/icons/**

• verified visreg changes with Terran (include link to visreg run/approval)
• all illustration/icons names have been reviewed by Dom and/or Terran

Change management

type=routine
risk=low
impact=sev5

automerge=false

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 1 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1
CODEOWNERS	✅ See below

✅ CODEOWNERS

Code Owner	Status	Calculation
ui-systems-eng-team	✅ 1/1	Denominator calculation Additional CODEOWNERS Requirement Show calculation Sum 0 0 From CODEOWNERS 1 Sum 1

[cb-ekuersch]

couple nits around documentation