fix(web): repo links land on prod, not the default branch (#880)

[aking526]

The bug

GitHub resolves a bare repository URL to the default branch, which on this
repo is main (gh api repos/ccb/agent-sandbox --jq .default_branch). So two of
the three links added in #984 were sending readers to main while the site is
built and deployed from prod:

Link	Before	After
Hero Code button	→ main	→ /tree/prod
"…in the repository"	→ main	→ /tree/prod
godot-generative-agents/README.md	/blob/prod/… (hand-typed)	repoFile(…)
BibTeX url	bare repo URL	unchanged, deliberately

The fix

home/links.ts owns the branch now:

const BRANCH = "prod";
export const repoTree = `${REPO_URL}/tree/${BRANCH}`;
export const repoFile = (path: string) => `${REPO_URL}/blob/${BRANCH}/${path}`;

One string to change on a rename, and a new link can't silently omit the branch.
The BibTeX url keeps the bare REPO_URL on purpose — a citation cites the
repository, not a branch that may not exist in five years.

CodeRef.tsx renders no anchor, so there was nothing else on the page to sweep.

The guard

links.test.ts pins both halves of the invariant: the helpers name prod, and no
component spells the repo URL out by hand instead of importing them. It globs its
sources via import.meta.glob(..., {query: '?raw'}), so a file added later is
covered without anyone remembering to list it — and it asserts the glob actually
matched HomeView.tsx/RunLocallySection.tsx, so a glob that silently matches
nothing can't make the rule vacuous.

Both rules mutation-checked, not just observed green:

• hard-coding https://github.com/ccb/agent-sandbox back into RunLocallySection
  → ./RunLocallySection.tsx builds repo links from links.ts fails.
• flipping BRANCH to "main" → both points … at prod tests fail.

Verification

• pnpm lint (0 errors), pnpm test 234 passed / 17 files, pnpm build clean.
• Grepped the built bundle rather than trusting a browser: it minifies to
  Vo="https://github.com/ccb/agent-sandbox", Rh="prod", Lh=${Vo}/tree/${Rh}, `op=e=>`${Vo}/blob/${Rh}/${e} — the branch is in every derived link, and zero
  occurrences of the retired aking526/penn-generative-agents remain.

Refs #880.

🤖 Generated with Claude Code