fix: rename em-dash asset filenames to ASCII hyphens

[didiergarcia]

Summary

• Renames two imagesets and their PNGs under Examples/apps/SegmentExtensionsExample/Assets.xcassets/ to drop em-dash (U+2014, —) characters in favor of ASCII hyphens (-).
• Updates the filename keys in both Contents.json files and the 4 image="..." / <image name="..."/> references in Main.storyboard that named them.

Why

GitHub's auto-generated source archive for each tag encodes the em-dashes as UTF-8 in ZIP entries. The default macOS unzip (Info-ZIP) can't decode those entries and aborts with:

checkdir error: cannot create .../Segment———Avatar———Green.imageset: Illegal byte sequence

The same extraction path is used by Xcode when resolving this package via SPM from a tag/archive, so downstream consumers see an "unzipping failed" error and can't install the package.

Repro (on stock macOS, before this fix):

curl -L https://github.com/segmentio/analytics-swift/archive/refs/tags/1.9.2.zip -o broken.zip
unzip broken.zip
# -> checkdir error: ... Illegal byte sequence

Fixes #431.

Scope

• Only 4 on-disk files renamed (imagesets + PNGs) using git mv so history is preserved.
• Only 6 text references updated — 2 in Contents.json, 4 in Main.storyboard.
• Nothing else in the repo referenced the em-dash paths (grep -rn $'—' . and find . -name '*—*' are both empty after this change).
• project.pbxproj is untouched — it references Assets.xcassets as a folder, not individual imagesets.
• No Swift source, no Package.swift, no SDK behavior changes.

Test plan

• Open Examples/apps/SegmentExtensionsExample/SegmentExtensionsExample.xcworkspace in Xcode, build + run on iOS Simulator, confirm both images still render (Twilio/Segment horizontal logo on splash, avatar on the main view).
• After tag/release: curl -L https://github.com/segmentio/analytics-swift/archive/refs/tags/<next>.zip -o test.zip && unzip test.zip completes cleanly with no Illegal byte sequence.
• In a fresh consumer project, resolve the package via SPM at the new tag and confirm no "unzipping failed" error.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.17%. Comparing base (b511158) to head (1466620).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #433      +/-   ##
==========================================
- Coverage   73.84%   73.17%   -0.68%     
==========================================
  Files          54       54              
  Lines        5425     4063    -1362     
==========================================
- Hits         4006     2973    -1033     
+ Misses       1419     1090     -329     

see 54 files with indirect coverage changes

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