feat(seer): Pass PR assignment flag and GitHub username to Seer

Add feature flag `organizations:seer-assign-prs-to-user` and wire it
through both autofix and explorer flows so Seer can assign PRs to the
invoking user on GitHub.

- Register feature flag in temporary.py
- Pass `assign_pr_to_user` in autofix request options
- Pass `github_username` and `assign_pr_to_user` in explorer user context

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Agent transcript: https://claudescope.sentry.dev/share/O_Pqf33_KzAdKIC0uHWtBHi4N9k2TWTCmGLf0e0rTrU

Author: JoshFerge

src/sentry/features/temporary.py

@@ -335,6 +335,8 @@ def register_temporary_features(manager: FeatureManager) -> None:
     manager.add("organizations:seer-slack-workflows", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enable Seer Explorer in Slack via @mentions
     manager.add("organizations:seer-slack-explorer", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
+    # Assign Seer-created PRs to the invoking user on GitHub
+    manager.add("organizations:seer-assign-prs-to-user", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=False)
     # Enable search query attribute validation
     manager.add("organizations:search-query-attribute-validation", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enable search query builder to support explicit boolean filters

src/sentry/seer/autofix/autofix.py

@@ -511,6 +511,9 @@ def _call_autofix(
                     "sentry:enable_seer_coding", default=ENABLE_SEER_CODING_DEFAULT
                 ),
                 "stopping_point": stopping_point.value if stopping_point else None,
+                "assign_pr_to_user": features.has(
+                    "organizations:seer-assign-prs-to-user", group.organization
+                ),
             },
             "preference": preference.dict() if preference else None,
         },

src/sentry/seer/explorer/client_utils.py

@@ -28,6 +28,7 @@
 from sentry.seer.models import SeerApiError
 from sentry.seer.seer_setup import has_seer_access_with_detail
 from sentry.seer.signed_seer_api import SeerViewerContext, make_signed_seer_api_request
+from sentry.seer.utils import get_github_username_for_user
 from sentry.users.models.user import User as SentryUser
 from sentry.users.services.user.model import RpcUser
 from sentry.users.services.user_option import user_option_service
@@ -284,13 +285,20 @@ def collect_user_org_context(
     # Get IP address from http request, if provided
     user_ip: str | None = request.META.get("REMOTE_ADDR") if request else None
 
+    # Resolve GitHub username for PR assignment/review
+    github_username = get_github_username_for_user(user, organization.id)
+
+    assign_pr_to_user = features.has("organizations:seer-assign-prs-to-user", organization)
+
     return {
         "org_slug": organization.slug,
         "user_id": user.id,
         "user_ip": user_ip,
         "user_name": user_name,
         "user_email": user.email,
         "user_timezone": user_timezone,
+        "github_username": github_username,
+        "assign_pr_to_user": assign_pr_to_user,
         "user_teams": user_teams,
         "user_projects": user_projects,
         "all_org_projects": all_org_projects,