fix(dependson): fallback to unsorted enqueue on circular dependency

[AruneshDwivedi]

fix(dependson): fallback to unsorted enqueue on circular dependency

When two or more Kustomizations referencing the same source form a dependsOn cycle, sortAndEnqueue in kustomization_indexers.go returns nil, which drops ALL reconciliation requests for that source — including Kustomizations not part of the cycle. This silently disables event-driven reconciliation for the entire source, with only a log line as evidence.

The topological ordering in sortAndEnqueue is an optimization. Out-of-order reconciles are already handled correctly by the DependencyNotReady requeue mechanism. Returning nil on sort error provides no correctness guarantee — a graceful fallback to unsorted enqueue loses nothing.

This PR changes sortAndEnqueue to fall back to unsorted enqueue when dependency.Sort returns an error (e.g. circular dependency), instead of dropping all requests.

Fixes #1712

[BUGFIX] Fix circular `dependsOn` silently disabling event-driven reconciliation for all Kustomizations sharing a source.

[Karthik-Chowdary]

The sortAndEnqueue fallback is directionally sound, but this PR currently includes a second, unrelated startup cleanup commit in main.go. That sweep deletes every directory matching $TMPDIR/kustomization-* without establishing ownership by this controller instance or checking whether another controller process is actively using it. Multiple controller instances can share /tmp (for example with a hostPath or other shared volume), and a newly starting instance could remove another live instance’s checkout. It is also unrelated to #1712 and has no tests here. Please drop the main.go commit from this PR and keep the circular-dependency fix focused; add a regression test that proves a sort error returns all original reconciliation requests rather than silently dropping them.