mAi: #133 — Verfahrensablauf duration affordance (hover + toggle)

t-paliad-302 / m/paliad#133. Surface each event card's rule duration
("2 Mo. nach") on /tools/verfahrensablauf — by default as a hover
tooltip on the date span, and optionally inline via a new
"Dauern anzeigen" header toggle (localStorage key
paliad.verfahrensablauf.durations-show).

The issue scoped this as pure-frontend on the assumption that the
duration fields were already on the /api/tools/fristenrechner payload.
They were not: lp.TimelineEntry exposed only the computed dueDate, not
the rule's (duration_value, duration_unit, timing) tuple. Added these
as three additive optional fields and populated them in both engine
emission sites (Calculate + CalculateByTriggerEvent) from the rule
row directly. Source values are the base rule fields, not the
post-alt-swap arithmetic — the tooltip reads as a property of the
rule rather than a recap of which branch fired.

Frontend wiring:
- formatDurationLabel() in verfahrensablauf-core builds the
  "<value> <unit> <timing>" string from the existing
  deadlines.event.unit.<unit>.{one,many} + deadlines.event.timing.*
  i18n keys, reused from /tools/fristenrechner's event-mode renderer.
- deadlineCardHtml attaches the label as title= on the date span
  (hover, default) and, when CardOpts.showDurations is on, emits an
  inline <span class="timeline-duration"> in the meta row.
- Court-set / zero-duration rules (trigger event, hearings) skip the
  affordance — durationValue <= 0 short-circuits in
  formatDurationLabel.
- Toggle persisted in localStorage under
  paliad.verfahrensablauf.durations-show, default off; sits next to
  the existing "Hinweise anzeigen" toggle.

bun run build clean, go test ./pkg/litigationplanner/... and
./internal/... clean, bun test src/client/views clean (89/89).

pkg/litigationplanner/types.go

@@ -371,6 +371,17 @@ type TimelineEntry struct {
 	ChoicesOffered   json.RawMessage   `json:"choicesOffered,omitempty"`
 	AppellantContext string            `json:"appellantContext,omitempty"`
 	IsHidden         bool              `json:"isHidden,omitempty"`
+	// DurationValue / DurationUnit / Timing surface the rule's
+	// arithmetic so /tools/verfahrensablauf can show "2 Mo. nach" on
+	// each event card (m/paliad#133, t-paliad-302). Source values from
+	// the Rule row (not the post-alt-swap arithmetic) — the tooltip
+	// reads as a property of the rule, not a recap of which branch
+	// fired. Zero-duration rules (root event, court-set) emit
+	// DurationValue=0 and the frontend suppresses the affordance.
+	// Timing is "before" | "after" — empty when r.Timing is NULL.
+	DurationValue int    `json:"durationValue,omitempty"`
+	DurationUnit  string `json:"durationUnit,omitempty"`
+	Timing        string `json:"timing,omitempty"`
 }
 
 // RuleCalculation is the single-rule calc response that backs the