feat(preprod): add watchos section + update code signature (#15538)

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## DESCRIBE YOUR PR
Adds a section explaining why watchOS apps may have unexpected size from
analysis. I also updated the Code Signature section to explain that code
signing also happens generally for the app.

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---------

Co-authored-by: Alex Krawiec <[email protected]>

Author: trevor-e

docs/platforms/apple/guides/ios/size-analysis/index.mdx

@@ -38,9 +38,13 @@ description: Upload iOS builds to Sentry for size analysis.
 
 <Include name="size-analysis/app-thinning" />
 
-### Binary Code Signature
+### WatchOS Architectures
 
-<Include name="size-analysis/binary-code-signature" />
+<Include name="size-analysis/watch-architecture-thinning" />
+
+### Code Signature
+
+<Include name="size-analysis/code-signature" />
 
 ### App Store Connect File Sizes
 

includes/size-analysis/binary-code-signature.mdx

@@ -0,0 +1,19 @@
+App bundles contain code signature data within `_CodeSignature/` directories. In these you'll find a `CodeResources` plist file with hashes of every file within the bundle. Similarly, Mach-O binaries contain additional hashes of every page block within its `LC_CODE_SIGNATURE` load command. This means the size of code signature data will scale linearly with the amount of files in your bundle and size of your binaries.
+
+By default Sentry calculates the size of this data as-is. You may notice differences when comparing against your app downloaded from the App Store. For example, Xcode 26 archives only codesign with `SHA256` hashes, but the App Store can use both `SHA1` and `SHA256` hashes. In other words, App Store downloads of your app may be slightly larger than what's produced by Xcode. This App Store behavior is subject to change at any time.
+
+If you'd like to compare the impact of this on your app, you can re-sign your app before uploading to Sentry:
+
+```bash
+# Inspect the current code signature
+codesign -dvvv '/path/to/your/app.app'
+
+# Re-sign with a new code signature
+codesign --force \
+  --sign 'Apple Distribution: Your Team (team_id)' \
+  --digest-algorithm sha1 \
+  --digest-algorithm sha256 \
+  '/path/to/your/app.app'
+```
+
+This will force both `SHA1` and `SHA256` hashes to be used.

includes/size-analysis/code-signature.mdx

@@ -0,0 +1 @@
+WatchOS apps produced by Xcode often contain both `arm64_32` and `arm64` architectures in a single fat binary. By default Sentry calculates the size of this data as-is, however, your end users will only download whatever architecture is necessary for their device. It's recommended to apply [App Thinning](/platforms/apple/guides/ios/size-analysis#app-thinning) before uploading for more representative results.