update actions to generate manifest.json

[tomjemmett]

Generate the manifest.json file in actions. cleans up the example Renviron which has some unused values in, and renames the environment used in the sync data step.

[Copilot]

Pull request overview

This PR moves manifest.json generation into GitHub Actions (via an R script) instead of maintaining it with Node scripts, and updates deployment/sync workflows and example environment configuration accordingly.

Changes:

• Remove the Node-based manifest update scripts and rely on rsconnect::writeManifest() for manifest generation.
• Update the reusable Connect publish workflow to generate/upload manifest.json and adjust environment/variable usage.
• Rename the GitHub Actions environment used by the sync-data job and tidy .Renviron.example.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
update_manifest.js	Deleted Node script previously used to update manifest.json.
remove_files_from_manifest.js	Deleted Node script that blanked manifest.json file entries.
dev/generate_manifest.R	Stops post-processing manifest; relies on rsconnect::writeManifest().
.Renviron.example	Removes unused example entries and reorders CACHE_VERSION.
.github/workflows/sync-data.yaml	Changes job environment from production to sync-data.
.github/workflows/connect-publish-prod.yaml	Adjusts environment naming passed to the reusable publish workflow.
.github/workflows/connect-publish-manual.yaml	Generates/uploads manifest in CI; broadens environment input handling; switches some values from secrets to vars.

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