Contraction: remove the pages/studio.ts shim and the stale leans/bulk remnants #393

Delete the 17-line src/web/pages/studio.ts re-export shim (point test/studio.test.ts at web/studio/words.ts), the unused latestLean in core/decisions.ts, and the comments that still name web/studio/leans.ts, bulkCss and a bulk bar/route that no longer exist.

Part of #386 (direction #334 §4). Acceptance: every old URL keeps answering (a redirect or the merged page) with a test per old route; the full forge.json check stays green; the pull states the line count dropped; docs/STUDIO.md and docs/DESIGN.md name only the surviving surfaces. Never touch the release workflow or the chart.

Declined: There's nothing left to do for #393. Commit 121d182 (#401) already did everything the issue asks for, so a pull from this branch would be empty.

• The shim: src/web/pages/studio.ts (17 lines) was deleted in #401, which also changed test/studio.test.ts to stop importing it.
• latestLean: #401 removed it from src/core/decisions.ts (43 lines changed there, almost all deletions).
• Stale comments: #401 also cleaned up the comments in src/web/studio/asks.ts and src/web/studio/style.ts. A search of src, test and docs now finds no mention of bulkCss, latestLean, web/studio/leans.ts or a bulk bar or route.
• Old URLs: The shim was a module, not a page address, so no URL went away with it. The one old address in this area, /big, already redirects to /board?wall, and test/board.test.ts has a test for each of its forms.
• Docs: Every source file that docs/STUDIO.md and docs/DESIGN.md name still exists. The only exceptions are src/lamp.ts and src/weather.ts, which appear in a made-up example screen in DESIGN.md, not as files in this repository.

Nothing was changed or pushed. Someone should close #393 as done by #401.

Parked by the crew: the run ended without a pull: declined: There's nothing left to do for #393. Commit 121d182 (#401) already did everything the issue asks for, so a pull from this branch would be empty.

Declined: Nothing has changed since the last run, so there is still nothing to push for #393. The new comment repeats my earlier decline and doesn't ask for anything new.

I fetched origin again just now. main has no new commits, src/web/pages/studio.ts doesn't exist, and src, test and docs contain no mention of latestLean, bulkCss or web/studio/leans.ts. Commit 121d182 (#401) did all of it. The only old address in this area, /big, already redirects to /board?wall, and test/board.test.ts tests each of its forms.

A pull from this branch would be empty. The fix is to close #393 as done by #401 rather than send it back to the crew. If something is still meant to be removed, the issue needs a comment naming the file or line, and I'll take it from there.

Parked by the crew: the run ended without a pull: declined: Nothing has changed since the last run, so there is still nothing to push for #393. The new comment repeats my earlier decline and doesn't ask for anything new.

Closing as done by #401 (commit 121d182). On main, src/web/pages/studio.ts is gone, and latestLean, bulkCss and web/studio/leans.ts appear nowhere in src, test or docs. /big redirects to /board?wall, and test/board.test.ts tests that redirect. Nothing is left to build.

Closing as shipped: src/web/pages/studio.ts is gone from main and nothing in src names latestLean, bulkCss or leans.ts. The rest of the contraction is #603 under P1.