chore(lint): adopt the canonical .golangci.yml from infra/ci-templates

Canonical lives at infra ci-templates/golangci.yml, distributed by the
infra#309 pattern: byte-identical copies, checksum drift gate in infra. Do
not edit this file here -- edit the canonical and run `task ci:sync`.

Verified locally before pushing, not pushed-and-hoped: golangci-lint v2.11.4
against a Go 1.26.1 toolchain (matching CI) reports 0 issues here.

Also applies gofumpt, which this config enables and the golangci-lint v2
default set does not check at all. That gap is why the drift was invisible:
earlier passes ran gofmt, which is weaker. Mechanical, deterministic,
build+vet verified.

ingestion/internal/capturehttp/handler_test.go

@@ -38,9 +38,11 @@ func (f fakeTracker) CreateIssue(context.Context, string, string, string) (captu
 	}
 	return capture.IssueRef{Repo: "hyperguild", Number: 1, URL: "https://git/1"}, nil
 }
+
 func (fakeTracker) CloseIssue(context.Context, string, int, string) (capture.IssueRef, error) {
 	return capture.IssueRef{}, nil
 }
+
 func (fakeTracker) CommentIssue(context.Context, string, int, string) (capture.IssueRef, error) {
 	return capture.IssueRef{}, nil
 }
@@ -183,6 +185,7 @@ type refusingAudit struct{}
 func (refusingAudit) Reserve(context.Context, classification.Level) (capture.AuditOutcome, error) {
 	return 0, errors.New("central audit sink unreachable")
 }
+
 func (refusingAudit) Record(context.Context, capture.AuditEntry, capture.AuditOutcome) error {
 	return nil
 }