[SHELL-0] Shell contracts and measurement #128

Tracking only. Each lane starts on an explicit owner GO.

Lane: SHELL-0 — first lane of the approved desktop shell direction.

Architecture: docs/architecture/DESKTOP_APPLICATION_SHELL_REVIEW.md (APP-ARCH-0, merged in #127).

Purpose

1. Define and unit-test first-party foundation contracts: application contributions, disposable lifecycle, renderer document-session boundary, application-service boundary, and command / panel / tool / contextual-panel / menu contribution boundaries. Foundation only — current callers are not migrated.
2. Measure the current application: cold start, Mall↔Editor and World↔Editor page-switch cost, memory (incl. a repeated round-trip soak), and a native-ESM file:// spike vs esbuild entry bundles, ending in one bundling recommendation.

Prerequisite for

• [UI-0-I2] Workspace behavior and command UX #121 — waits for SHELL-0 only.
• [UI-0-M] Application menu command bridge #122 — waits for the SHELL-0 command/menu boundary.

Out of scope

Persistent shell, mall:describe, main.js decomposition, navigation hardening (Shell-1b), renderer path-authority fixes (future SEC-SHELL-0), application menu (#122), workspace behavior (#121), docking (UI-C0/UI-1), WD2-E, visual redesign. No new dependency. No repository-policy change.

Acceptance

• Contract modules + focused tests
• Reproducible startup / page-switch / memory baselines with machine-readable results
• ESM spike + esbuild comparison + recommendation
• docs/architecture/SHELL_0_CONTRACTS_AND_MEASUREMENTS.md
• npm run check passes; no user-facing behavior change