Revise Feature and Experiment Lifecycle documentation

[jeffpaul]

What?

Updated document to clarify the definitions and processes for Features and Experiments, including promotion criteria and UI presentation.

Relates to #234.

Copilot summary

This pull request updates the documentation to clarify the lifecycle and distinction between Features and Experiments in the AI plugin. The changes provide more explicit guidance on how Features and Experiments are defined, promoted, and evaluated, making the process clearer for contributors and users.

Feature and Experiment definitions and lifecycle:

• The document was renamed from EXPERIMENT_LIFECYCLE.md to FEATURE_EXPERIMENT_LIFECYCLE.md and rewritten to explain the difference between Features (stable, supported functionality) and Experiments (early-stage, subject to breaking changes), including how each is surfaced in the UI and registered in the codebase.
• Added a section detailing the criteria and process for promoting an Experiment to a Feature, including stability, user value, UX maturity, technical reliability, and maintainability.

Process and evaluation updates:

• Clarified that proposals to WordPress core can focus on either a Feature or an Experiment, not just Experiments, and referenced core merge criteria.
• Added notes emphasizing that Features are expected to be stable and supported, while Experiments can be deprecated or removed at any time and may undergo breaking changes, typically signaled by a major version bump.

Why?

How?

Use of AI Tools

Testing Instructions

Testing Instructions for Keyboard

Screenshots or screencast

Before	After

[github-actions]

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Co-authored-by: jeffpaul <[email protected]>

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.85%. Comparing base (0d1ec92) to head (37bace0).

Additional details and impacted files

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##             develop     #326   +/-   ##
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  Coverage      57.85%   57.85%           
  Complexity       615      615           
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  Files             46       46           
  Lines           3165     3165           
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  Hits            1831     1831           
  Misses          1334     1334           

Flag	Coverage Δ
unit	57.85% <ø> (ø)

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