Remove ContextSource::File — all identity in store now

Identity files migrated to memory nodes:
- identity, core-personality, reflections, where-am-i

Removed:
- ContextSource::File enum variant
- File source parsing and handling
- load_memory_file helper function

Config now only supports Store and Journal sources.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/cli/node.rs

@@ -190,13 +190,6 @@ pub async fn get_group_content(group: &crate::config::ContextGroup, cfg: &crate:
             }
             results
         }
-        crate::config::ContextSource::File => {
-            group.keys.iter().filter_map(|key| {
-                let content = std::fs::read_to_string(cfg.identity_dir.join(key)).ok()?;
-                if content.trim().is_empty() { return None; }
-                Some((key.clone(), content.trim().to_string()))
-            }).collect()
-        }
         crate::config::ContextSource::Store => {
             let mut results = Vec::new();
             for key in &group.keys {