[eas-cli] Add PostHog GraphQL layer and command utils

[gwdp]

Why

Plumbing for the posthog commands — GraphQL layer + shared utils.

How

• PostHogQuery + PostHogMutation + fragments/types
• commandUtils/posthog.ts (dashboard URL, formatter)
• generated.ts from the universe schema

Test Plan

• CI
• Live integration needs the universe PostHog backend deployed

[github-actions]

⏩ The changelog entry check has been skipped since the "no changelog" label is present.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.43%. Comparing base (9d1a6b7) to head (cabef9c).
⚠️ Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3835      +/-   ##
==========================================
+ Coverage   58.23%   58.43%   +0.20%     
==========================================
  Files         916      917       +1     
  Lines       39727    39999     +272     
  Branches     8324     8419      +95     
==========================================
+ Hits        23133    23368     +235     
- Misses      15159    16536    +1377     
+ Partials     1435       95    -1340     

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