fix(portrayal): map VERCSA → verticalClearanceSafe ("sf clr" labels)

The S-101 catalogue models a feature's safe vertical clearance as the complex
attribute verticalClearanceSafe; CableOverhead (and the other overhead rules)
already emit the "sf clr %4.1f" label from it. But our S-57→S-101 attribute
bridge synthesized only VERCCL/VERCLR/VERCOP/HORCLR — VERCSA was never mapped,
so verticalClearanceSafe was always nil and the rule's safe-clearance branches
fell through. Overhead cables/pipes carrying VERCSA (no VERCLR) showed just the
dashed line with no clearance text.

Add verticalClearanceSafe ← VERCSA to the clearances map. Verified on S-64 cell
AA5DBASE (§3.1 Base, ref p100): now emits "sf clr 15.0" ×3 alongside "clr 10.0"
×3, matching the reference plot. Same class of S-101-model gap as the bridge
vertical-clearance fix. Needs a re-bake.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: beetlebugorg

internal/engine/s101/host.go

@@ -207,12 +207,14 @@ func (e *Engine) bindHost() {
 }
 
 // clearances maps each S-101 clearance complex attribute to the S-57 simple
-// attribute that backs it and the value sub-attribute the rules read. Bridges
-// carry clearances as S-57 simple attributes (VERCCL/VERCLR/HORCLR/VERCOP); the
-// S-101 catalogue models them as complex attributes wrapping a *Value field.
+// attribute that backs it and the value sub-attribute the rules read. Bridges and
+// overhead cables/pipes carry clearances as S-57 simple attributes
+// (VERCCL/VERCLR/VERCSA/HORCLR/VERCOP); the S-101 catalogue models them as complex
+// attributes wrapping a *Value field.
 var clearances = map[string]struct{ s57, value string }{
 	"verticalClearanceClosed":  {"VERCCL", "verticalClearanceValue"},
 	"verticalClearanceFixed":   {"VERCLR", "verticalClearanceValue"},
+	"verticalClearanceSafe":    {"VERCSA", "verticalClearanceValue"},
 	"verticalClearanceOpen":    {"VERCOP", "verticalClearanceValue"},
 	"horizontalClearanceFixed": {"HORCLR", "horizontalClearanceValue"},
 }