[codex] add app and package boundaries

[dbtlr]

Summary

Adds the second Saga foundation phase: explicit app package boundaries, initial shared package skeletons, and enforceable dependency-direction lint rules.

Changes

• Added app packages for @saga/cli, @saga/service, and @saga/control-plane.
• Added initial shared package skeletons for contracts, runtime, db, core, claims, active-context, mcp, collectors, and connectors.
• Updated Turbo placeholder build outputs for no-emit TypeScript package checks.
• Expanded Vite+/Oxlint no-restricted-imports rules to enforce app/package boundaries and UI dependency isolation.

Validation

• pnpm run verify
• pnpm run build

Mimir

Completed phase SGA-6 with tasks SGA-7, SGA-8, and SGA-9.