personas: elevate to server with per-persona fact scoping

Move personas off the mobile client into ImageApi as first-class
records, and scope entity_facts by persona so each one builds its own
voice over a shared entity graph. The new include_all_memories flag
lets a persona opt back into the full hive-mind pool for human
browsing of /knowledge/*; agentic generation always stays in-voice.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/bin/populate_knowledge.rs

@@ -335,6 +335,7 @@ async fn main() -> anyhow::Result<()> {
                 None,
                 Vec::new(),
                 Vec::new(),
+                "default".to_string(),
             )
             .await
         {