Update monthly release workflow for new asset naming

[cderv]

The daily build now produces platform-specific filenames (rstudio/tinytex#484, rstudio/tinytex#486):

• TinyTeX-1-linux-x86_64.tar.xz, TinyTeX-1-darwin.tar.xz, TinyTeX-1-windows.exe, etc.
• Legacy names (TinyTeX-1.tar.gz, .tgz, .zip) are still produced as backward-compat copies

The monthly workflow currently works — v2026.04 will be fine as-is. But some things need attention.

What works today

The sed rename pattern handles both old and new names correctly. All assets download and rename without issues.

What should be updated now

1. monthly-notes.md — Currently says "zip for Windows, tgz for macOS, tar.gz for Linux". Needs to document the new naming scheme and new platforms (ARM64, musl). PR Document ARM64 Linux bundles in README and release notes #52 partially addresses this but was written before the full naming change landed.

2. Redundant assets — Monthly releases will contain both old and new names for the same content (~double the files). We could optionally clean up legacy files after download to keep releases clean. Not harmful, just redundant.

What breaks if legacy names are removed from daily

If we removes the legacy copies from the daily build (per #37 comment, they're temporary):

1. md5sum TinyTeX-1.zip (line 72) — TinyTeX-1.zip won't exist. Needs to switch to the new Windows asset name. See Adapt Chocolatey package for .exe-only Windows bundles #54 for related Chocolatey changes.

2. Chocolatey URL — The .zip download URL in chocolateyinstall.ps1 would break. See Adapt Chocolatey package for .exe-only Windows bundles #54.

Context: rstudio/tinytex#483, rstudio/tinytex#484, rstudio/tinytex#486, rstudio/tinytex#487, #37

[yihui]

The choco issues should be resolved now. Future choco packages will use .exe. Removing legacy names won't affect the choco package because if users choose to install an old version of the choco package, choco will find the .zip files from older TinyTeX monthly releases (these .zip links were hardcoded in the older choco packages).

Now the main reason to keep the legacy names is for older versions of Quarto to be able to install the latest monthly release. I guess it should be reasonable to remove the legacy names after two years.