feat: Wikidata engine and Wikipedia knowledge infobox

- Add wikidata engine (wbsearchentities), tests, factory/planner/config
- Wikipedia REST summary: infobox from extract, thumbnail, article URL
- InfoboxView URL; render infobox list in results_inner + base styles
- Preferences Wikidata toggle; engine badge color for wikidata

Made-with: Cursor

internal/engines/wikidata.go

@@ -0,0 +1,133 @@
+// samsa — a privacy-respecting metasearch engine
+// Copyright (C) 2026-present metamorphosis-dev
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+package engines
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"github.com/metamorphosis-dev/samsa/internal/contracts"
+)
+
+// wikidataAPIBase is the Wikidata MediaWiki API endpoint (overridable in tests).
+var wikidataAPIBase = "https://www.wikidata.org/w/api.php"
+
+// WikidataEngine searches entity labels and descriptions via the Wikidata API.
+// See: https://www.wikidata.org/w/api.php?action=help&modules=wbsearchentities
+type WikidataEngine struct {
+	client *http.Client
+}
+
+func (e *WikidataEngine) Name() string { return "wikidata" }
+
+func (e *WikidataEngine) Search(ctx context.Context, req contracts.SearchRequest) (contracts.SearchResponse, error) {
+	if e == nil || e.client == nil {
+		return contracts.SearchResponse{}, errors.New("wikidata engine not initialized")
+	}
+	q := strings.TrimSpace(req.Query)
+	if q == "" {
+		return contracts.SearchResponse{Query: req.Query}, nil
+	}
+
+	lang := strings.TrimSpace(req.Language)
+	if lang == "" || lang == "auto" {
+		lang = "en"
+	}
+	lang = strings.SplitN(lang, "-", 2)[0]
+	lang = strings.ReplaceAll(lang, "_", "-")
+	if _, ok := validWikipediaLangs[lang]; !ok {
+		lang = "en"
+	}
+
+	u, err := url.Parse(wikidataAPIBase)
+	if err != nil {
+		return contracts.SearchResponse{}, err
+	}
+	qv := u.Query()
+	qv.Set("action", "wbsearchentities")
+	qv.Set("search", q)
+	qv.Set("language", lang)
+	qv.Set("limit", "10")
+	qv.Set("format", "json")
+	u.RawQuery = qv.Encode()
+
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
+	if err != nil {
+		return contracts.SearchResponse{}, err
+	}
+	httpReq.Header.Set("User-Agent", "samsa/1.0 (Wikidata search; +https://github.com/metamorphosis-dev/samsa)")
+
+	resp, err := e.client.Do(httpReq)
+	if err != nil {
+		return contracts.SearchResponse{}, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		io.Copy(io.Discard, io.LimitReader(resp.Body, 16*1024))
+		return contracts.SearchResponse{}, fmt.Errorf("wikidata upstream error: status %d", resp.StatusCode)
+	}
+
+	body, err := io.ReadAll(io.LimitReader(resp.Body, 2*1024*1024))
+	if err != nil {
+		return contracts.SearchResponse{}, err
+	}
+
+	var api struct {
+		Search []struct {
+			ID          string `json:"id"`
+			Label       string `json:"label"`
+			Description string `json:"description"`
+		} `json:"search"`
+	}
+	if err := json.Unmarshal(body, &api); err != nil {
+		return contracts.SearchResponse{}, fmt.Errorf("wikidata JSON parse error: %w", err)
+	}
+
+	results := make([]contracts.MainResult, 0, len(api.Search))
+	for _, hit := range api.Search {
+		id := strings.TrimSpace(hit.ID)
+		if id == "" || !strings.HasPrefix(id, "Q") {
+			continue
+		}
+		pageURL := "https://www.wikidata.org/wiki/" + url.PathEscape(id)
+		title := strings.TrimSpace(hit.Label)
+		if title == "" {
+			title = id
+		}
+		content := strings.TrimSpace(hit.Description)
+		urlPtr := pageURL
+		results = append(results, contracts.MainResult{
+			Template: "default.html",
+			Title:    title,
+			Content:  content,
+			URL:      &urlPtr,
+			Engine:   "wikidata",
+			Category: "general",
+			Engines:  []string{"wikidata"},
+		})
+	}
+
+	return contracts.SearchResponse{
+		Query:               req.Query,
+		NumberOfResults:     len(results),
+		Results:             results,
+		Answers:             []map[string]any{},
+		Corrections:         []string{},
+		Infoboxes:           []map[string]any{},
+		Suggestions:         []string{},
+		UnresponsiveEngines: [][2]string{},
+	}, nil
+}