chore: slim CLAUDE.md and extract swift-testing skill

[grdsdev]

Summary

• Replace the @AGENTS.md include (317 lines loaded every session) with a focused 20-line CLAUDE.md containing only what's non-derivable from the code
• Extract Swift Testing conventions into .claude/skills/swift-testing/skill.md — pulled on demand via /swift-testing instead of loaded every session

What was removed from always-on context

• Project structure (derivable via ls Sources/)
• Build commands (in scripts/)
• Dependency list (in Package.swift)
• Architecture prose, CI details, support policy, common task workflows

What was kept / moved

Content	Where
Format before commit, xcodebuild preference, PR-only rule, conventional commits	CLAUDE.md (always-on)
Swift Testing conventions, Replay vs Mocker, @Suite/#expect rules, SDK-435 context	.claude/skills/swift-testing/skill.md (on-demand)

[coveralls]

Coverage Report for CI Build 29026458343

Coverage increased (+0.2%) to 83.221%

Details

• Coverage increased (+0.2%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• 6 coverage regressions across 2 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

6 previously-covered lines in 2 files lost coverage.

File	Lines Losing Coverage	Coverage
Sources/Auth/Internal/Keychain.swift	5	37.23%
Sources/Auth/Storage/KeychainLocalStorage.swift	1	41.67%

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Coverage Stats

Relevant Lines:	9470
Covered Lines:	7881
Line Coverage:	83.22%
Coverage Strength:	37.59 hits per line

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💛 - Coveralls