Download DMRG scripts from ALPSim/ALPS instead of vendoring them

[marcusr2ML]

Brings the DMRG series in line with the DMFT and MCS tutorials: the scripts are fetched from ALPSim/ALPS instead of being copied into this repo.

What changed

• The 26 download links in dmrg03–dmrg06 now point at raw.githubusercontent.com/ALPSim/ALPS/master/tutorials/... and use the shared alps-download.js handler, so a click saves the file instead of navigating the reader to GitHub.
• The 27 vendored copies under content/en/tutorials/dmrg/codes/ are removed.
• Adds assets/js/alps-download.js and wires it up in layouts/baseof.html.

Tracking master rather than a pinned commit means the tutorials always serve the current source. The trade-off is deliberate: if a file is renamed upstream the link 404s instead of silently serving a stale snapshot, which is the failure mode you want to hear about.

Verification

• All 27 vendored files were byte-identical to their master counterparts before removal, so readers get exactly the same bytes from the canonical source.
• All 26 new URLs confirmed to return 200 on master.
• Nothing else in the repo referenced dmrg/codes/.
• Clean hugo --gc --minify --cleanDestinationDir build: 26 anchors render (dmrg03: 10, dmrg04: 5, dmrg05: 7, dmrg06: 4), no stale codes/ output.

Scope: English only

The Japanese and Chinese DMRG pages are deliberately untouched, and they need a separate content pass rather than a URL rewrite.

They are already broken on the live site: 9 of their 23 link targets point at tutorials/dmrg-01-dmrg/... on master, which no longer exists after the upstream folder rename, so those are live 404s today. The remaining 14 are pinned to bd842d1 and still resolve, but serve pre-rename content.

Remapping the URLs would not be enough for DMRG-05. The English page is 293 lines across 17 sections after the restructure; the translations are 127 lines across 8, and still walk the reader through spin_one and spin_one.py, which the English version no longer uses at all — it uses spin_one_uniform, spin_one_capped, and build_lattice.py. Pointing those links at the new files would leave the prose describing one file while the button downloads another.

DMRG-03/04/06 match the English structure and name the same files, so those would remap cleanly whenever the translation pass happens.

Note for merging

Two other open PRs (#138 MCS, #139 DMFT) add the same assets/js/alps-download.js and the same layouts/baseof.html block. Whichever merges first will make the other two conflict on those two files — identical content, so resolution is trivial, but it will come up.

🤖 Generated with Claude Code

[marcusr2ML]

@Ooolab Same deal as before. I just wanted to give you a heads up that the en DMRG-05 is much different than the translations as of now. It needed a lot of work over the weekend.

[egull]

I like this much better than the previous solution, but @Ooolab should also weigh in (and possibly @afeiguin who has the final say over all things DMRG)

[marcusr2ML]

@egull I'll wait for Fei. I'll add Adrian as a reviewer, but might merge if we are waiting too long for a follow up.

Also, I simply made Claude do the updates. I think it duplciated the JS I gave it. Will clean up today.