GHSA-cr4g-f395-h25h

## Summary

PR #37698 added checkDownloadTokenScope to /raw/*, /media/*, and attachment download web endpoints. The /archive/* endpoint (repo.Download in routers/web/repo/repo.go:372) was not included in the fix. This endpoint accepts OAuth2 tokens via webAuth.AllowOAuth2 (registered at routers/web/web.go:1649-1652) but does not call checkDownloadTokenScope or CheckRepoScopedToken.

A personal access token with any non-repository scope (e.g., read:issue or read:misc) can download full repository archives (zip/tar.gz) of private repositories the token owner has access to.

## Impact

Scope escalation: tokens scoped to non-repository categories can access full repository content through the archive download endpoint. Higher impact than endpoints fixed in #37698 because /archive/* serves the entire repository.

## Steps to Reproduce

1. Create a personal access token with ONLY read:misc scope 2. Access: GET /{owner}/{private-repo}/archive/main.tar.gz 3. Archive is served (200 OK) instead of being rejected (403 Forbidden)

Compare with fixed endpoints: - GET /{owner}/{private-repo}/raw/branch/main/README.md correctly returns 403

## Root Cause

Download function in routers/web/repo/repo.go:372 does not call checkDownloadTokenScope. The outer group middleware reqUnitCodeReader checks repository permission but not token scope.

The API equivalent (/api/v1/repos/{owner}/{repo}/archive/*) IS properly scoped via tokenRequiresScopes(AccessTokenScopeCategoryRepository). The git HTTP endpoints are scoped via CheckRepoScopedToken in httpBase.

## Suggested Fix

Add checkDownloadTokenScope(ctx) to Download and InitiateDownload in routers/web/repo/repo.go. The function already exists in routers/web/repo/download.go (same package).

## Discovery Method

Variant analysis of PR #37698 — reviewed all web routes with webAuth.AllowOAuth2 middleware.