feat: add TemplateBuilderCreateTemplate SDK types and client method (#26360)

Adds `POST /api/v2/templatebuilder/compose/template`, a synchronous
endpoint that composes a template from a base and modules, validates it
via a provisioner import job, and creates the template in a single
request.

The handler composes terraform files, bundles them as a tar, inserts the
file with hash-based dedup, creates a template version with an import
job, waits up to 2 minutes for the job to complete, classifies errors
for known failure modes (network-unreachable registry, DNS failures),
then creates the template on success. Canceled and failed jobs return
appropriate error responses.

Also adds `hclwrite.Format` to composed terraform output for canonical
HCL formatting.

Closes https://linear.app/codercom/issue/DEVEX-279

<details>
<summary>Implementation notes</summary>

- SDK types and client method in `codersdk/templatebuilder.go` with
validation tags matching the standard template creation path
(`template_display_name`, `lt=128`)
- `ClassifyProvisionerError` in `coderd/templatebuilder/errors.go`
detects DNS, connection refused, i/o timeout, and TLS handshake failures
and returns actionable messages
- `waitForProvisionerJob` polls with a ramp-up interval schedule (100ms,
200ms, 500ms, then 1s steady) and accepts an `onUpdate` callback for
future SSE streaming
- Audit logging for both template and template version creation
- TOCTOU name uniqueness: early check for fast feedback, DB unique
constraint catch for the race window (returns 409, not 500)
- Swagger annotations for all error responses (400, 404, 409, 504)

</details>

> 🤖 Generated by Coder Agents

codersdk/templatebuilder.go

@@ -6,6 +6,8 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+
+	"github.com/google/uuid"
 )
 
 // TemplateBuilderVariableType enumerates the variable types
@@ -124,3 +126,37 @@ func (c *Client) TemplateBuilderCompose(ctx context.Context, req TemplateBuilder
 	}
 	return io.ReadAll(res.Body)
 }
+
+// TemplateBuilderCreateTemplateRequest is the request body for
+// POST /api/v2/templatebuilder/compose/template.
+type TemplateBuilderCreateTemplateRequest struct {
+	BaseTemplateID  string                         `json:"base_template_id"`
+	Modules         []TemplateBuilderComposeModule `json:"modules"`
+	OrganizationID  uuid.UUID                      `json:"organization_id" format:"uuid" validate:"required"`
+	Name            string                         `json:"name" validate:"required,template_name"`
+	DisplayName     string                         `json:"display_name,omitempty" validate:"template_display_name"`
+	Description     string                         `json:"description,omitempty" validate:"lt=128"`
+	Icon            string                         `json:"icon,omitempty"`
+	ProvisionerTags map[string]string              `json:"provisioner_tags,omitempty"`
+}
+
+// TemplateBuilderCreateTemplateResponse is the response body for
+// POST /api/v2/templatebuilder/compose/template.
+type TemplateBuilderCreateTemplateResponse struct {
+	Template Template `json:"template"`
+}
+
+// TemplateBuilderCreateTemplate composes a template from a base and modules,
+// validates it via a provisioner import job, and creates the template.
+func (c *Client) TemplateBuilderCreateTemplate(ctx context.Context, req TemplateBuilderCreateTemplateRequest) (TemplateBuilderCreateTemplateResponse, error) {
+	res, err := c.Request(ctx, http.MethodPost, "/api/v2/templatebuilder/compose/template", req)
+	if err != nil {
+		return TemplateBuilderCreateTemplateResponse{}, err
+	}
+	defer res.Body.Close()
+	if res.StatusCode != http.StatusCreated {
+		return TemplateBuilderCreateTemplateResponse{}, ReadBodyAsError(res)
+	}
+	var resp TemplateBuilderCreateTemplateResponse
+	return resp, json.NewDecoder(res.Body).Decode(&resp)
+}