uploads: centralise via ChatHubApi::save_upload, refactor handlers

Extract shared upload seam in skald-core, move Telegram and web
handlers to use it. Simplify media attachment routing. Clean up
unused deps and dead code.

crates/skald-core/src/session/handler/mod.rs

@@ -20,7 +20,7 @@ use crate::config::DatetimeConfig;
 use crate::db::{chat_history, chat_sessions_stack};
 use crate::events::ServerEvent;
 use core_api::message_meta::MessageMetadata;
-use core_api::user_fs::SharedFs;
+use core_api::user_fs::{SharedFs, UserFs};
 use crate::llm::LlmManager;
 use crate::mcp::McpProvider;
 use crate::image_generate::ImageGeneratorManager;
@@ -414,6 +414,13 @@ impl ChatSessionHandler {
         }
     }
 
+    /// The caller's current filesystem snapshot (home + shared folders + projects
+    /// + docs). Cheap — clones an `Arc`. Used by upload persistence to place files
+    /// in the owner's home.
+    pub fn user_fs(&self) -> Arc<UserFs> {
+        self.fs.load()
+    }
+
     /// Override the session used for scratchpad reads/writes.
     /// Called by the cron runner for async tasks so they share the parent's scratchpad.
     pub fn set_scratchpad_session_id(&self, id: i64) {