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>

server/handlers/forms.go

@@ -0,0 +1,63 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+
+	"armature/forms"
+)
+
+// FormsHandler provides REST endpoints for the standalone forms system.
+type FormsHandler struct{}
+
+// formsValidateRequest is the request body for POST /api/v1/forms/validate.
+type formsValidateRequest struct {
+	Template json.RawMessage        `json:"template"`
+	Data     map[string]interface{} `json:"data"`
+}
+
+// formsValidateResponse is the response body for POST /api/v1/forms/validate.
+type formsValidateResponse struct {
+	Valid  bool              `json:"valid"`
+	Errors []forms.FieldError `json:"errors"`
+}
+
+// Validate validates form data against a typed form template.
+//
+//	POST /api/v1/forms/validate
+//	Body: { "template": {...}, "data": {...} }
+//	Response: { "valid": true/false, "errors": [...] }
+func (h *FormsHandler) Validate(c *gin.Context) {
+	var req formsValidateRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid request body"})
+		return
+	}
+
+	if len(req.Template) == 0 {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "template is required"})
+		return
+	}
+
+	tpl := forms.ParseTypedFormTemplate(req.Template)
+	if tpl == nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "template is invalid or empty"})
+		return
+	}
+
+	if req.Data == nil {
+		req.Data = make(map[string]interface{})
+	}
+
+	errs := forms.ValidateFormData(tpl, req.Data)
+	if errs == nil {
+		errs = []forms.FieldError{}
+	}
+
+	c.JSON(http.StatusOK, formsValidateResponse{
+		Valid:  len(errs) == 0,
+		Errors: errs,
+	})
+}