Upstream tags pollute origin remote

## Problem

Multiple scripts and CI workflows use `git fetch --tags` or `git push --tags` without scoping, causing ~900 upstream OpenCode tags to leak into our origin remote. Deleting them manually doesn't help — they reappear on the next fetch/push cycle.

## Impact

- 952 tags on origin, only 7 are ours
- Release pages show incorrect changelogs
- Confusing tag namespace