fix: remove consumed annotations from analysis registry

[DerManoMann]

Summary

• Adds Analysis::removeAnnotation() as a proper API for removing annotations from the analysis registry — removes from both SplObjectStorage and $context->annotations array (full inverse of addAnnotation)
• MergeJsonContent and MergeXmlContent now fully clean up after consuming annotations:
  • Remove from analysis registry
  • Update _context to reflect the new parent (MediaType), so tree-walking validation sees the annotation in the correct location
• Replaces all direct $analysis->annotations->offsetUnset() calls across processors (AugmentRefs, AugmentTags, BuildPaths, MergeIntoOpenApi) with the new method for consistency
• Adds ADR-001 documenting context keys and the annotation lifecycle contract for processors

Background

After converting JsonContent into MediaType + schema, the processor removed it from $parent->_unmerged but:

1. Left it in the analysis's SplObjectStorage and $context->annotations
2. Left _context->nested pointing at the old parent

When validation walks the tree via collectAnnotations(), it finds the JsonContent (reused as MediaType->schema) and validates it. With the stale context, this could produce spurious "Unexpected @OA\JsonContent()" warnings — particularly for annotations created dynamically by processors.

Test plan

• Full test suite passes (1037 tests, 12,937,597 assertions)
• Verify no orphan JsonContent/XmlContent warnings with dynamically-created annotations (openapi-extras integration)

🤖 Generated with Claude Code

[github-actions]

Created backport PR for 5.x:

• [Backport #2024 to 5.x] fix: remove consumed annotations from analysis registry #2025 with remaining conflicts!

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin backport-2024-to-5.x
git worktree add --checkout .worktree/backport-2024-to-5.x backport-2024-to-5.x
cd .worktree/backport-2024-to-5.x
git reset --hard HEAD^
git cherry-pick -x 060af3bb9c4cba6a5859aba2c51cd1c129479410