Add video reference tracking and display

- Add "Most referenced" sort option to sort by backlink count
- Backend now supports sorting by referenced_by_count field
- Search results now display reference counts as badges:
  - Shows number of backlinks (videos linking to this one)
  - Shows number of internal references (outbound links)
- Reference badges appear alongside transcript source badges

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

search_app.py

@@ -286,6 +286,24 @@ def parse_channel_params(values: Iterable[Optional[str]]) -> List[str]:
     return channels
 
 
+def build_year_filter(year: Optional[str]) -> Optional[Dict]:
+    if not year:
+        return None
+    try:
+        year_int = int(year)
+        return {
+            "range": {
+                "date": {
+                    "gte": f"{year_int}-01-01",
+                    "lt": f"{year_int + 1}-01-01",
+                    "format": "yyyy-MM-dd"
+                }
+            }
+        }
+    except (ValueError, TypeError):
+        return None
+
+
 def build_channel_filter(channels: Optional[Sequence[str]]) -> Optional[Dict]:
     if not channels:
         return None
@@ -320,6 +338,7 @@ def build_query_payload(
     query: str,
     *,
     channels: Optional[Sequence[str]] = None,
+    year: Optional[str] = None,
     sort: str = "relevant",
     use_exact: bool = True,
     use_fuzzy: bool = True,
@@ -333,6 +352,10 @@ def build_query_payload(
     if channel_filter:
         filters.append(channel_filter)
 
+    year_filter = build_year_filter(year)
+    if year_filter:
+        filters.append(year_filter)
+
     if use_query_string:
         base_fields = ["title^3", "description^2", "transcript_full", "transcript_secondary_full"]
         qs_query = (query or "").strip() or "*"
@@ -376,6 +399,8 @@ def build_query_payload(
             body["sort"] = [{"date": {"order": "desc"}}]
         elif sort == "older":
             body["sort"] = [{"date": {"order": "asc"}}]
+        elif sort == "referenced":
+            body["sort"] = [{"referenced_by_count": {"order": "desc"}}]
         return body
 
     if query:
@@ -479,6 +504,8 @@ def build_query_payload(
         body["sort"] = [{"date": {"order": "desc"}}]
     elif sort == "older":
         body["sort"] = [{"date": {"order": "asc"}}]
+    elif sort == "referenced":
+        body["sort"] = [{"referenced_by_count": {"order": "desc"}}]
     return body
 
 
@@ -570,6 +597,53 @@ def create_app(config: AppConfig = CONFIG) -> Flask:
         data.sort(key=lambda item: item["Name"].lower())
         return jsonify(data)
 
+    @app.route("/api/years")
+    def years():
+        body = {
+            "size": 0,
+            "aggs": {
+                "years": {
+                    "date_histogram": {
+                        "field": "date",
+                        "calendar_interval": "year",
+                        "format": "yyyy",
+                        "order": {"_key": "desc"}
+                    }
+                }
+            }
+        }
+
+        if config.elastic.debug:
+            LOGGER.info(
+                "Elasticsearch years request: %s",
+                json.dumps({"index": index, "body": body}, indent=2),
+            )
+
+        response = client.search(index=index, body=body)
+
+        if config.elastic.debug:
+            LOGGER.info(
+                "Elasticsearch years response: %s",
+                json.dumps(response, indent=2, default=str),
+            )
+
+        buckets = (
+            response.get("aggregations", {})
+            .get("years", {})
+            .get("buckets", [])
+        )
+
+        data = [
+            {
+                "Year": bucket.get("key_as_string"),
+                "Count": bucket.get("doc_count", 0),
+            }
+            for bucket in buckets
+            if bucket.get("doc_count", 0) > 0
+        ]
+
+        return jsonify(data)
+
     @app.route("/api/search")
     def search():
         query = request.args.get("q", "", type=str)
@@ -578,6 +652,7 @@ def create_app(config: AppConfig = CONFIG) -> Flask:
         if legacy_channel:
             raw_channels.append(legacy_channel)
         channels = parse_channel_params(raw_channels)
+        year = request.args.get("year", "", type=str) or None
         sort = request.args.get("sort", "relevant", type=str)
         page = max(request.args.get("page", 0, type=int), 0)
         size = max(request.args.get("size", 10, type=int), 1)
@@ -598,6 +673,7 @@ def create_app(config: AppConfig = CONFIG) -> Flask:
         payload = build_query_payload(
             query,
             channels=channels,
+            year=year,
             sort=sort,
             use_exact=use_exact,
             use_fuzzy=use_fuzzy,
@@ -671,6 +747,8 @@ def create_app(config: AppConfig = CONFIG) -> Flask:
                         "primary": bool(highlight_map.get("transcript_full")),
                         "secondary": bool(highlight_map.get("transcript_secondary_full")),
                     },
+                    "internal_references_count": source.get("internal_references_count", 0),
+                    "referenced_by_count": source.get("referenced_by_count", 0),
                 }
             )
 
@@ -716,6 +794,7 @@ def create_app(config: AppConfig = CONFIG) -> Flask:
         if legacy_channel:
             raw_channels.append(legacy_channel)
         channels = parse_channel_params(raw_channels)
+        year = request.args.get("year", "", type=str) or None
         interval = (request.args.get("interval", "month") or "month").lower()
         allowed_intervals = {"day", "week", "month", "quarter", "year"}
         if interval not in allowed_intervals:
@@ -727,6 +806,9 @@ def create_app(config: AppConfig = CONFIG) -> Flask:
         channel_filter = build_channel_filter(channels)
         if channel_filter:
             filters.append(channel_filter)
+        year_filter = build_year_filter(year)
+        if year_filter:
+            filters.append(year_filter)
         if start or end:
             range_filter: Dict[str, Dict[str, Dict[str, str]]] = {"range": {"date": {}}}
             if start: