refactor: establish Fetch folder feature

[jderochervlk]

Tracking issue: #342

Stack context

Part 9 of the Option 5 folder-feature stack.

• Previous: refactor: establish CSSFontLoading folder feature #318
• Next: the File folder consolidation layer

Review this PR as the incremental diff against #318.

Summary

• rename src/Fetch to the target src/fetch folder
• retain the complete folder on the existing unqualified internal Fetch feature
• preserve the supported WebAPI.Fetch dependency closure through Event, File, and URL
• leave all flat Fetch interface module paths unchanged

The internal FetchTypes helper remains private within the folder.

Temporary state

• this PR does not introduce compatibility aliases, exclusions, or module slices; the Fetch folder and feature ownership are final
• the File dependency is still backed by the pre-consolidation File folders and core helpers; the next layer completes that ownership

Review focus

• physical folder ownership only
• preservation of the existing WebAPI.Fetch implication and public module paths
• complete folder membership

Verification

• node_modules/.bin/rescript clean
• node_modules/.bin/rescript build --prod --features DOM,Event,File,URL,Fetch
• npm run build
• npm test
• npm run format:check
• git diff --check

[jderochervlk]

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Update Fetch's documentation lookup after moving the folder

When the API docs are generated, docs/utils.js derives each source directory from featureSpecs, where Fetch is still recorded as Fetch, so it probes src/Fetch/FetchTypes.res. After this change moves the source to src/fetch, the existsSync filter silently removes Fetch from apiModules, causing the generated API index and routes to omit the entire Fetch API. Update the shared feature metadata or documentation discovery to use the new path.

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