feat: discoverability (NodeInfo, hashtags) and moderation (domain/actor blocking)

- NodeInfo at /.well-known/nodeinfo + /nodeinfo/2.0
- Hashtags #MoviesDiary + #MovieTitle on review posts; /tags/{tag} redirect
- Domain blocking: blocked_domains table, admin API + HTML, inbox enforcement
- Per-actor blocking: blocked_actors table, user API + HTML, BlockActivity send/receive
- Delivery filter excludes blocked actors and blocked-domain inboxes

crates/adapters/activitypub-base/src/nodeinfo.rs

@@ -0,0 +1,119 @@
+use activitypub_federation::config::Data;
+use axum::Json;
+use serde::Serialize;
+
+use crate::data::FederationData;
+use crate::error::Error;
+
+#[derive(Serialize)]
+pub struct NodeInfoWellKnown {
+    pub links: Vec<NodeInfoLink>,
+}
+
+#[derive(Serialize)]
+pub struct NodeInfoLink {
+    pub rel: String,
+    pub href: String,
+}
+
+#[derive(Serialize)]
+pub struct NodeInfoSoftware {
+    pub name: String,
+    pub version: String,
+}
+
+#[derive(Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct NodeInfoUsage {
+    pub users: NodeInfoUsers,
+    pub local_posts: u64,
+}
+
+#[derive(Serialize)]
+pub struct NodeInfoUsers {
+    pub total: usize,
+}
+
+#[derive(Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct NodeInfo {
+    pub version: String,
+    pub software: NodeInfoSoftware,
+    pub protocols: Vec<String>,
+    pub usage: NodeInfoUsage,
+    pub open_registrations: bool,
+}
+
+pub async fn nodeinfo_well_known_handler(
+    data: Data<FederationData>,
+) -> Result<Json<NodeInfoWellKnown>, Error> {
+    let href = format!("{}/nodeinfo/2.0", data.base_url);
+    Ok(Json(NodeInfoWellKnown {
+        links: vec![NodeInfoLink {
+            rel: "http://nodeinfo.diaspora.software/ns/schema/2.0".to_string(),
+            href,
+        }],
+    }))
+}
+
+pub async fn nodeinfo_handler(
+    data: Data<FederationData>,
+) -> Result<Json<NodeInfo>, Error> {
+    let user_count = data.user_repo.count_users().await.unwrap_or(0);
+    let local_posts = data.object_handler.count_local_posts().await.unwrap_or(0);
+
+    Ok(Json(NodeInfo {
+        version: "2.0".to_string(),
+        software: NodeInfoSoftware {
+            name: data.software_name.clone(),
+            version: env!("CARGO_PKG_VERSION").to_string(),
+        },
+        protocols: vec!["activitypub".to_string()],
+        usage: NodeInfoUsage {
+            users: NodeInfoUsers { total: user_count },
+            local_posts,
+        },
+        open_registrations: data.allow_registration,
+    }))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn nodeinfo_well_known_serializes_correctly() {
+        let doc = NodeInfoWellKnown {
+            links: vec![NodeInfoLink {
+                rel: "http://nodeinfo.diaspora.software/ns/schema/2.0".to_string(),
+                href: "https://example.com/nodeinfo/2.0".to_string(),
+            }],
+        };
+        let json = serde_json::to_value(&doc).unwrap();
+        assert_eq!(json["links"][0]["rel"], "http://nodeinfo.diaspora.software/ns/schema/2.0");
+        assert_eq!(json["links"][0]["href"], "https://example.com/nodeinfo/2.0");
+    }
+
+    #[test]
+    fn nodeinfo_serializes_camel_case() {
+        let doc = NodeInfo {
+            version: "2.0".to_string(),
+            software: NodeInfoSoftware {
+                name: "my-app".to_string(),
+                version: "0.1.0".to_string(),
+            },
+            protocols: vec!["activitypub".to_string()],
+            usage: NodeInfoUsage {
+                users: NodeInfoUsers { total: 3 },
+                local_posts: 42,
+            },
+            open_registrations: false,
+        };
+        let json = serde_json::to_value(&doc).unwrap();
+        assert_eq!(json["version"], "2.0");
+        assert_eq!(json["software"]["name"], "my-app");
+        assert_eq!(json["usage"]["users"]["total"], 3);
+        assert_eq!(json["usage"]["localPosts"], 42);
+        assert_eq!(json["openRegistrations"], false);
+    }
+}