feat(search): P3.1 filters and multi-query merge

Native include/exclude domains, time_range, topic, exact_match, min_score,
and up to 4 queries fused with RRF. Honesty notes stay off the Warn/fail
path. Tavily keeps include_answer false and sets auto_parameters false.
Cache key is canonical JSON. CLI flags and skill recipe included.

internal/search/types.go

@@ -25,22 +25,37 @@ var sourceRank = map[string]int{
 
 // Hit is one search result after mapping. No page body, no vendor answers.
 type Hit struct {
-	URL     string  `json:"url"`
-	Title   string  `json:"title"`
-	Snippet string  `json:"snippet"`
-	Score   float64 `json:"score"`
-	Source  string  `json:"source"`
+	URL           string  `json:"url"`
+	Title         string  `json:"title"`
+	Snippet       string  `json:"snippet"`
+	Score         float64 `json:"score"`
+	Source        string  `json:"source"`
+	PublishedDate string  `json:"published_date,omitempty"`
+}
+
+// Filter is native search knobs. The zero value is P3 behaviour.
+type Filter struct {
+	IncludeDomains     []string
+	ExcludeDomains     []string
+	IncludeDomainsMode string // restrict | prefer; empty means restrict when include is set
+	TimeRange          string // day|week|month|year
+	StartDate          string
+	EndDate            string
+	Topic              string // general|news|finance; empty means general
+	ExactMatch         bool
+	MinScore           float64
 }
 
 // Source is one upstream. Config-fixed endpoint; never a request URL.
 type Source interface {
 	Name() string
-	Search(ctx context.Context, query string, k int) SourceOut
+	Search(ctx context.Context, query string, k int, f Filter) SourceOut
 }
 
 type SourceOut struct {
 	Hits    []Hit
-	Warn    string
+	Warn    string   // failure only (timeout, HTTP error, pin)
+	Notes   []string // honesty: filters not applied, recall loss
 	Credits int
 }
 
@@ -80,6 +95,7 @@ func Dedupe(in []Hit) []Hit {
 			continue
 		}
 		if s, ok := seen[canon]; ok {
+			keepDate := firstDate(s.h.PublishedDate, h.PublishedDate)
 			if len(h.Snippet) > len(s.h.Snippet) {
 				src := s.h.Source
 				keep := s.h.URL
@@ -91,6 +107,7 @@ func Dedupe(in []Hit) []Hit {
 					s.h.Score = sc
 				}
 			}
+			s.h.PublishedDate = keepDate
 			continue
 		}
 		cp := h
@@ -104,6 +121,13 @@ func Dedupe(in []Hit) []Hit {
 	return out
 }
 
+func firstDate(a, b string) string {
+	if a != "" {
+		return a
+	}
+	return b
+}
+
 func sortBySourceOrder(hits []Hit) {
 	sort.SliceStable(hits, func(i, j int) bool {
 		ri, rj := sourceRank[hits[i].Source], sourceRank[hits[j].Source]