feat(web): add automatic actions for open pull requests

A new pr_open alert carries the head commit SHA of each open, non-draft, same-repository pull request. An action with auto enabled sends its webhook once for each pull request and head commit. An authors list limits which pull requests trigger it. The alert never changes repository health.

internal/gh/fetch.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"net/url"
 	"slices"
+	"strings"
 	"time"
 
 	"github.com/lukaszraczylo/ghtracker/internal/model"
@@ -129,8 +130,12 @@ func (c *Client) openPRs(ctx context.Context, full string) ([]model.PullRequest,
 		HTMLURL   string    `json:"html_url"`
 		User      userRef   `json:"user"`
 		Head      struct {
-			SHA string `json:"sha"`
+			Repo *repoRef `json:"repo"`
+			SHA  string   `json:"sha"`
 		} `json:"head"`
+		Base struct {
+			Repo *repoRef `json:"repo"`
+		} `json:"base"`
 		Labels []labelRef `json:"labels"`
 		Number int        `json:"number"`
 		Draft  bool       `json:"draft"`
@@ -141,13 +146,22 @@ func (c *Client) openPRs(ctx context.Context, full string) ([]model.PullRequest,
 	for _, p := range items {
 		out = append(out, model.PullRequest{
 			Number: p.Number, Title: p.Title, URL: p.HTMLURL, Author: p.User.Login, Draft: p.Draft,
-			Labels: labelNames(p.Labels), HeadSHA: p.Head.SHA, CreatedAt: p.CreatedAt, UpdatedAt: p.UpdatedAt,
+			Labels: labelNames(p.Labels), HeadSHA: p.Head.SHA, Fork: isFork(p.Head.Repo, p.Base.Repo), CreatedAt: p.CreatedAt, UpdatedAt: p.UpdatedAt,
 			Checks: model.CheckSummary{State: model.ChecksUnknown},
 		})
 	}
 	return out, err
 }
 
+type repoRef struct {
+	FullName string `json:"full_name"`
+}
+
+// isFork reports a head repo that differs from the base repo; a deleted head repo counts as a fork.
+func isFork(head, base *repoRef) bool {
+	return head == nil || base == nil || !strings.EqualFold(head.FullName, base.FullName)
+}
+
 // attachChecks fills each PR's check summary; it reports the first failure but still tries every PR.
 func (c *Client) attachChecks(ctx context.Context, full string, prs []model.PullRequest) error {
 	var first error