Studio app structure: layout decision and the mechanical move #1777

Parent: #1774.

Scope

Re-shape the apps/ layout for five feature stacks instead of a skeleton, as a decision plus a no-behaviour-change move.

• Today: apps/{contracts,server,web} with web/src/{components/{shell,ui},features,lib,routes} — sized for the bootstrap skeleton (shell, auth gate, connection banner). Chat, schedules, knowledge, settings, and search (Studio chat: sessions, streamed runs, controls, chat workspace #1747–Studio global search palette and keyboard-shortcuts reference #1751) land on top of it.
• Questions to settle: feature-sliced vs layer-first in apps/web; where domain hooks and cross-surface state live; whether apps/contracts stays one package or splits Zod schemas from the generated client; whether the BFF's routes/ + mecatl/ + auth/ split holds at five surfaces; whether the workspace stays apps/ now that it holds exactly one app.
• Delivery shape: the decision first, then one mechanical PR with no behaviour change — pure moves and import rewrites, so the diff is reviewable and git log --follow survives. Generated files (routeTree.gen.ts, apps/contracts/src/generated/*) are regenerated, never hand-moved.

Human decisions

• Feature-sliced or layer-first in apps/web?
• apps/ or studio/ as the workspace root? (affects the studio CI relevance category, task studio:*, .dockerignore, the release job, and every doc path)
• Does apps/contracts split?

Contract

docs/acceptance/studio-app-structure.md (Bounded — a structure decision with a mechanical move; no interface change, but the paths are a contract every later PR and doc citation depends on). Classified at plan time per docs/development-process.md.

Verification

task studio:check and #1767's integration suite green unchanged across the move (the proof that it is mechanical); task docs for the doc-path citations; task ac-trace for the plan proofs. Lands before the e2e work (#1776) so journeys are not written twice, and before or alongside the agent contract (#1775) so the contract documents the final layout.