feat(litigationplanner): appeal-target synthetic trigger row + appeal-role stamping (t-paliad-307, m/paliad#136)

Engine side of the four Verfahrensablauf appeal bugs in m/paliad#136.

Bug 2 — Missing trigger event row. When CalcOptions.AppealTarget is set,
Calculate now prepends a synthetic TimelineEntry to the deadlines slice
dated to the trigger date, carrying the per-appeal-target label from
TriggerEventLabelForAppealTarget (Endentscheidung (R.118), Kosten-
entscheidung, Anordnung, Schadensbemessung, Bucheinsicht). Marked
IsRootEvent + IsTriggerEvent + party=court + priority=informational
so the frontend renders it as a dimmed anchor card without a save
button / choices caret / click-to-edit affordance. Empty Code so it
doesn't collide with real rule UUIDs downstream.

Bug 1 (engine half) — Side selector dead on appeal. Every appeal
filing rule carries primary_party='both' in the catalog, so the
column bucketer couldn't distinguish Berufungskläger vs Berufungs-
beklagter filings from primary_party alone. Engine now stamps the
new TimelineEntry.AppealRole field with appellant/appellee from the
rule-semantic AppealFilerRole mapping (appeal_role.go) when an
appeal_target is in scope. The frontend half of the fix (next commit)
consumes this to route each "both" rule into the user-perspective
column once the user picks a side.

Mapping covers all 12 appeal filing rules across the three
applies_to_target tracks (endentscheidung/schadensbemessung,
kostenentscheidung, anordnung/bucheinsicht). Court-issued events
(merits.decision, merits.oral, cost.decision, order.order) stay
empty — they continue to route on Party='court'. Unmapped
submission_codes return empty so a new appeal rule we forgot to map
falls through to the bucketer's legacy path rather than silently
picking a side.

Tests: TestAppealFilerRole pins the mapping; TestCalculate_Appeal
SyntheticTriggerRow covers (a) synthetic row prepended + AppealRole
stamped when target is set, (b) no synthetic row + no AppealRole
when target is unset (regression guard), (c) unknown target
short-circuits to no-op. Existing tests untouched — both behaviours
gate on opts.AppealTarget != "".

No DB migration — the bugs are calc-side. deadline_rules untouched.

pkg/litigationplanner/engine.go

@@ -572,6 +572,21 @@ func Calculate(
 		deadlines = append(deadlines, d)
 	}
 
+	// Stamp AppealRole on every entry when an appeal-target filter is
+	// active so the frontend column-bucketer can route primary_party=
+	// 'both' rules into the user-perspective columns
+	// (Berufungskläger vs Berufungsbeklagter). Court events stay empty
+	// — they route on Party='court' regardless. (t-paliad-307 /
+	// m/paliad#136 Bug 1)
+	if opts.AppealTarget != "" && IsValidAppealTarget(opts.AppealTarget) {
+		for i := range deadlines {
+			if deadlines[i].Code == "" {
+				continue
+			}
+			deadlines[i].AppealRole = AppealFilerRole(deadlines[i].Code)
+		}
+	}
+
 	// Restore sequence_order on the output slice. The compute walk
 	// re-ordered rules topologically (parent-first) so the parent-state
 	// checks resolved correctly; the wire shape and the linear timeline
@@ -594,6 +609,31 @@ func Calculate(
 	// same-group rows. Court-set / conditional rows sort LAST.
 	sortDeadlinesByDurationWithinTriggerGroup(deadlines, ruleByID)
 
+	// Synthetic trigger-event row for appeal timelines (t-paliad-307 /
+	// m/paliad#136 Bug 2). The decision being appealed (Endentscheidung
+	// R.118, Kostenentscheidung, Anordnung, …) isn't a rule in the
+	// upc.apl catalog — it's the anchor the user picked. Lawyers expect
+	// it to surface as the first row of the timeline so the chain reads
+	// decision → appeal filings → next decision. Emitted only when an
+	// appeal_target is in play and the helper returns a non-empty label.
+	if opts.AppealTarget != "" && IsValidAppealTarget(opts.AppealTarget) {
+		nameDE := TriggerEventLabelForAppealTarget(opts.AppealTarget, "de")
+		nameEN := TriggerEventLabelForAppealTarget(opts.AppealTarget, "en")
+		if nameDE != "" || nameEN != "" {
+			trig := TimelineEntry{
+				Name:           nameDE,
+				NameEN:         nameEN,
+				Party:          PrimaryPartyCourt,
+				Priority:       "informational",
+				DueDate:        triggerDateStr,
+				OriginalDate:   triggerDateStr,
+				IsRootEvent:    true,
+				IsTriggerEvent: true,
+			}
+			deadlines = append([]TimelineEntry{trig}, deadlines...)
+		}
+	}
+
 	resp := &Timeline{
 		ProceedingType:   pickedProceeding.Code,
 		ProceedingName:   pickedProceeding.Name,