Fix Homebrew tap publish credential for Release workflow

[cbusillo]

Objective

Allow the Release workflow to push generated Formula/Code.rb updates to just-every/homebrew-tap instead of only warning and continuing.

Current Status

State: Waiting
Next action: Configure a cross-repo credential that can write to just-every/homebrew-tap, or change the tap publishing model to use a PR/pull workflow.
Blocked by: GitHub credential/access setup outside this repository.
Last verified: 2026-05-24 in Release run 26360477400.

Evidence

Release run 26360477400 generated the Homebrew formula for v0.6.100, but the push to just-every/homebrew-tap failed with:

remote: Permission to just-every/homebrew-tap.git denied to github-actions[bot].
fatal: unable to access ... The requested URL returned error: 403

PR #118 made this non-fatal so GitHub Releases can proceed while tap credentials are repaired.

Acceptance Criteria

• Release workflow can push formula updates to just-every/homebrew-tap, or opens a durable tap PR instead.
• The workflow log no longer emits the tap 403 warning on a release run.
• The Homebrew formula points at the current GitHub Release assets and checksums.

Relationships

Follow-up from #118 and the v0.6.100 release validation work.
Related to #85 and #87.

[cbusillo]

Planning update from 2026-05-24:

Homebrew publishing is no longer considered required for the near-term auto-update plan. The current direction is to use GitHub Releases as the canonical internal update feed, with #127 generating a release manifest and #128 adding guarded CLI update behavior.

This issue should remain deferred unless we later decide package-manager distribution is intentional. If #126 removes Homebrew publishing from the active Release path, this issue can likely be closed as superseded rather than fixed with a cross-repo credential.