Feat v0.9.5 typed forms SDK primitive

Extract typed form system from models/workflow.go into standalone
server/forms/ package. Any package can now declare and validate
forms, not just workflow stages.

- New server/forms/ package (types + validation + condition evaluator)
- REST POST /api/v1/forms/validate endpoint
- Starlark forms.validate(template, data) module
- Frontend sw.forms.render(), .validate(), .validateRemote()
- Manifest form_template accepted at package level
- 16 new tests (12 forms + 4 Starlark module)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/PACKAGE-FORMAT.md

@@ -75,6 +75,7 @@ Only `manifest.json` is required. All other directories are optional and include
 | `contributes` | Slot contributions this package injects into other surfaces |
 | `capabilities` | Environment requirements: `{"required": [...], "optional": [...]}` |
 | `schema_version` | Integer for additive schema migrations |
+| `form_template` | Typed form template (v0.9.5). Fields array or fieldsets for progressive forms. Validated at install. |
 
 ## Multi-Surface Packages