Schema Builder UI (th studio) for local THS authoring

[snissn]

Background

For dev/PoC users, authoring raw THS JSON is still high-friction. We need a local-first schema builder that accelerates iteration without introducing managed-platform complexity.

Goal

Deliver a local th studio schema builder focused on rapid THS authoring + validation + preview.

Scope

• Add th studio command that launches a local web UI.
• Visual editor for app metadata, collections, fields, rules, and indexes.
• Real-time structural validation + semantic lints from packages/schema.
• Save/load THS JSON from disk.
• Show generated route and contract surface preview (informational, no full codegen required in v1).

Non-goals (v1)

• Multi-user collaboration.
• Hosted backend/API.
• Auth/account features.

Implementation Notes

• Reuse current schema/lint packages directly (no forked validation logic).
• Prefer local filesystem writes with explicit save actions.
• Keep architecture extendable for a future managed Studio.

Acceptance Criteria

• th studio launches a local editor and can create a valid THS file end-to-end.
• Validation/lint errors are shown with actionable field-level messages.
• User can open existing THS file, edit, and save.
• Preview panel shows expected collection routes and key generated functions.

[snissn]

Resolved by PR #48 (merged): added th studio local schema builder UI with load/save/validate/preview and integration coverage.