fix: correct tryCatch handler signature and make flow-typed install non-fatal

[Copilot]

Two distinct CI failures on main are addressed here: a broken tryCatch error handler that surfaces only when shiny is absent (e.g. check-depends-only mode), and a postinstall.sh step that hard-fails whenever the flow-typed GitHub cache fetch encounters an API error.

Changes

• R/shinyModule.R — test_shiny_version() used error = function() with no parameters. R passes the caught condition as the first argument to handlers; a zero-parameter handler throws unused argument (cond) instead of returning FALSE. Only manifests when shiny is not installed (Suggests, not Imports).

# before
tryCatch({ ... }, error = function() { FALSE })

# after
tryCatch({ ... }, error = function(e) { FALSE })

• bin/postinstall.sh — flow-typed install fetches a type-definition cache from the GitHub API; transient failures (rate limits, network errors) caused the entire yarn install to abort. Appended || true to make it non-fatal.

yarn flow-typed install --skip true --ignoreDeps dev || true

Note: The third failure (macOS-latest (4.6.0) — HTTP 404 downloading R) is a transient CRAN publishing lag: R 4.6.0 was released 2026-04-24 and the macOS binary was not yet available when the check ran three days later. No code change needed.

[karangattu]

Closing as a duplicate Copilot draft. Keeping #103 as the canonical PR for the package-check failure tracked in #102.