fix: unify resample policy target-points table

The policy -> target-points mapping existed twice with different values:
internal/config (300/600/1000) fed the resampler's MinimumRequiredPoints
threshold, while internal/metricdispatch (200/500/1000) fed the requested
resolution and the frontend target point count.

Because the threshold was larger than the target, the resampler refused to
downsample series whose length fell between the two numbers, silently
dropping the resolution the backend had asked for. With the medium policy
that covered every series between 500 and 600 points.

Move the table into internal/config as the single source of truth (import
direction rules out the reverse, since metricdispatch already imports
config) and keep the 200/500/1000 values, which already drove the requested
resolution. metricdispatch.TargetPointsForPolicy now delegates to it, so
MinimumRequiredPoints equals the target and resampling happens exactly when
a series exceeds it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

internal/config/config_test.go

@@ -10,6 +10,7 @@ import (
 
 	ccconf "github.com/ClusterCockpit/cc-lib/v2/ccConfig"
 	cclog "github.com/ClusterCockpit/cc-lib/v2/ccLogger"
+	"github.com/ClusterCockpit/cc-lib/v2/resampler"
 )
 
 func TestInit(t *testing.T) {
@@ -39,3 +40,46 @@ func TestInitMinimal(t *testing.T) {
 		t.Errorf("wrong addr\ngot: %s \nwant: 127.0.0.1:8080", Keys.Addr)
 	}
 }
+
+func TestTargetPointsForPolicy(t *testing.T) {
+	tests := []struct {
+		policy string
+		want   int
+	}{
+		{"low", 200},
+		{"medium", 500},
+		{"high", 1000},
+		{"unknown", 0},
+		{"", 0},
+	}
+
+	for _, tt := range tests {
+		if got := TargetPointsForPolicy(tt.policy); got != tt.want {
+			t.Errorf("TargetPointsForPolicy(%q) = %d, want %d", tt.policy, got, tt.want)
+		}
+	}
+}
+
+// The resampler must be allowed to act exactly when a series exceeds the target
+// point count. A mismatch here silently drops resample requests for a band of
+// job durations.
+func TestInitSyncsResamplerThreshold(t *testing.T) {
+	for _, policy := range []string{"low", "medium", "high"} {
+		Keys.EnableResampling = &ResampleConfig{DefaultPolicy: policy}
+		initResampler()
+
+		want := TargetPointsForPolicy(policy)
+		if resampler.MinimumRequiredPoints != want {
+			t.Errorf("policy %q: MinimumRequiredPoints = %d, want %d",
+				policy, resampler.MinimumRequiredPoints, want)
+		}
+	}
+
+	// Empty policy falls back to the documented default.
+	Keys.EnableResampling = &ResampleConfig{}
+	initResampler()
+	if want := TargetPointsForPolicy(DefaultResamplePolicy); resampler.MinimumRequiredPoints != want {
+		t.Errorf("empty policy: MinimumRequiredPoints = %d, want %d",
+			resampler.MinimumRequiredPoints, want)
+	}
+}