The /packs list and a pack's page speak the home page's language #9776

Part of the design pass that already covered /explore, /apps and /forges. A pack is how a newcomer starts from a premade forge, so its pages are often the first thing someone reads.

Done looks like:

• [x] /packs and /packs/:name (src/web/pages/packs.ts) follow the principles that open docs/DESIGN.md, as the /apps pass (985ca3e57) did: one heading, what the pack brings in a sentence, and the one command or button to start it shown first, with nothing ahead of it.
• [x] At 390 px wide neither page scrolls sideways. The pack command wraps or scrolls inside its own box.
• [x] test/packs.test.ts, test/packs-hands.test.ts and test/packs-up.test.ts pass. If one has to change, the pull says why.
• [x] A warm request still answers under 50 ms, and both pages work with JavaScript off.
• [x] bun scripts/design-lint.ts passes. Any new class goes in an area doc under docs/design/areas/, not docs/DESIGN.md.

Files: src/web/pages/packs.ts. Risks: the start command is shown verbatim. It stays escaped, and the page keeps printing the forge's real host and never makes one up.

Reviewed pull #9785 at its head: ticked /packs and /packs/:name (src/web/pages/packs.ts) follow the principles that open docs/DESIGN.md, as the /apps pass (985ca3e57) did: one heading, what the pack brings in a sentence, and the one command or button to start it shown first, with nothing ahead of it.; At 390 px wide neither page scrolls sideways. The pack command wraps or scrolls inside its own box.; test/packs.test.ts, test/packs-hands.test.ts and test/packs-up.test.ts pass. If one has to change, the pull says why.; A warm request still answers under 50 ms, and both pages work with JavaScript off.; bun scripts/design-lint.ts passes. Any new class goes in an area doc under docs/design/areas/, not docs/DESIGN.md..