Contraction: one codebase, fewer frames — fold /big, the dev app page, landing and the no-JS search into studio and board; remove the TUI's app/run/crew and origins twins #386

Direction #334 §4. Studio and dev are one codebase behind a forge_mode cookie. Fold: /big (src/web/pages/big.ts, ~2.2k lines) into the board as the one wall mode; the dev app page (pages/apps.ts) into the studio app page keeping only its environment controls; landing/site into the studio home's empty state; the no-JS search page into the search route. Remove: the TUI's apps, runs and crew screens and its origins group (web origins and migrate STAY — they are how businesses come in); the stale leans/bulk remnants and the 17-line pages/studio.ts shim. Keep first-class: the TUI workspace, editor and review over SSH; the dev code surface (browse, file, explorer, editor, commits, diff, pull review).

Acceptance per run (split this into one issue per fold/removal and link them here):

• [ ] each fold keeps every URL answering (a redirect or the merged page), with a test per old route
• [ ] the full check stays green; line counts drop and the number says so in the pull
• [ ] docs/STUDIO.md and docs/DESIGN.md name the surviving surfaces only

Mason fits this. Never touch the release workflow or the chart.