fix: git push hook post receive - #38089

* fix incorrect delayWriter call (there is already a defer call)
* split HookPostReceive into small functions
* fix incorrect HookPostReceiveResult response for errors
* fix incorrect AddRepoToLicenseUpdaterQueue call
* make sure repo home and branches page can work without default branch
* make sure default branch is always synchronized between database and
git repo, and fix FIXME

…s/v1.27

Conflict: routers/private/default_branch.go was deleted upstream by
go-gitea/gitea#38965 (backport of #38964, "remove dead code
SetDefaultBranch"). Accepted the deletion: the DCS
ProcessDoor43MetadataForRepo() call it held had been unreachable since
go-gitea/gitea#38089 removed the last caller of the internal
set-default-branch endpoint, and both default-branch-change paths are
already covered by the metadataNotifier ChangeDefaultBranch and
PushCommits hooks. Dropped the stale row from dcs-customizations.md.

Assisted-by: Claude Code:claude-opus-5[1m]

Conflicts and DCS adaptations for this upstream sync:

routers/private/default_branch.go: deleted upstream by go-gitea/gitea#38964
("remove dead code SetDefaultBranch"). Accepted the deletion. The DCS
ProcessDoor43MetadataForRepo() call it held had been unreachable since
go-gitea/gitea#38089 removed the last caller of the internal
set-default-branch endpoint; both default-branch-change paths are already
covered by the metadataNotifier ChangeDefaultBranch and PushCommits hooks.
Dropped the stale row from dcs-customizations.md.

modules/gitrepo -> modules/git/gitrepo (go-gitea/gitea#38543), with
OpenRepository/UpdateRef/RemoveRef moving to modules/git and
OpenRepository gaining a leading ctx: adapted services/gitref,
services/convert2sb, services/repository/sbarchiver,
services/door43metadata and services/door43healthcheck.

Repository.RepoPath() and repo_model.RepoPath() removed
(go-gitea/gitea#38601): replaced with
gitrepo.RepoLocalPath(x.CodeStorageRepo()).

util.RemoveAll renamed to util.RemoveAllWithRetry (go-gitea/gitea#38588).

Form validation refactor (go-gitea/gitea#38832, #38873): the DCS
Door43Metadata forms did only default validation, so they now embed
middleware.FormDefaultValidator instead of defining a Validate method.

web.GetForm and cron RegisterTaskFatal became generic: updated the DCS
git-ref handlers and DCS cron task registrations.

language_stats_gogit.go deleted upstream (gogit build variant removed);
git carried the DCS every-file-type language stats into the surviving
language_stats_get.go via rename detection.

Upstream enabled the forcetypeassert linter, which surfaced 28
unchecked type assertions in pre-existing DCS manifest and langnames
parsing. Added modules/dcs/mapvalue.go with checked map accessors and
used them throughout, so malformed user-supplied manifest.yaml or
langnames data yields zero values instead of panicking.

Verified: go build ./..., go vet ./..., golangci-lint run ./... (0
issues), lint-spell, lint-templates, generate-swagger (DCS git-ref
endpoints and the new in-catalog/tag_filter params intact, no dangling
$refs).

Assisted-by: Claude Code:claude-opus-5[1m]