refactor: replace long arg lists with input/config structs and builder

- Thought::new_local → NewThought struct (7 args → 1)
- UserWriter::update_profile → UpdateProfileInput struct (6 args → 2)
- update_profile use case → UpdateProfileInput (8 args → 3)
- ActivityPubService::new → builder pattern (9 args → 5 required + 4 optional setters)
- accept_note → AcceptNoteInput struct (8 args → 1)
- ThoughtNote::new_public → ThoughtNoteInput struct (8 args → 1)

Remove all #[allow(clippy::too_many_arguments)] annotations.

crates/domain/src/models/user.rs

@@ -1,6 +1,15 @@
 use crate::value_objects::{Email, PasswordHash, UserId, Username};
 use chrono::{DateTime, Utc};
 
+#[derive(Debug, Default, Clone)]
+pub struct UpdateProfileInput {
+    pub display_name: Option<String>,
+    pub bio: Option<String>,
+    pub avatar_url: Option<String>,
+    pub header_url: Option<String>,
+    pub custom_css: Option<String>,
+}
+
 #[derive(Debug, Clone)]
 pub struct User {
     pub id: UserId,