chore: standardize file headers and refresh stale documentation

[weskcode]

Summary

Repository hygiene, no code changes.

File headers. Xcode's default header template had stamped a tool name rather than the author into 36 sources. These now follow the repo's existing convention, Created by Wesley Keetch on <date>, with the original dates preserved.

Stale documentation. Three public-facing claims had drifted from reality:

Claim	Was	Now
README requirements table	Minimum iOS 26.0	Minimum iOS 26.5 (matches IPHONEOS_DEPLOYMENT_TARGET)
README toolchain note	"currently builds against the Xcode 27 beta"	Builds with Xcode 26; also compiles against the 27 beta
CONTRIBUTING first contributions	"Extract strings into a String Catalog (none exists yet)"	The catalog exists and ships English + Spanish, so this offers adding a locale instead

Gitignore. Adds *.xcresult so local test-result bundles are never committed.

Verification

• git grep finds no remaining tool-name headers
• xcodebuild build-for-testing (SunHatUnitTests scheme, iPhone 17 Pro sim) succeeds
• README's stated minimum now matches the project's actual deployment target

🤖 Generated with Claude Code

[weskcode]

Superseded by #12 — this PR's head branch was renamed to chore/standardize-file-headers, which closed this one automatically. Same commit, plus stale-documentation fixes.