public: strip PII from source — Casey refs, home path, email, creds in gitignore

Replace real name, email, and gendered pronouns in doc comments with
neutral phrasing ("the user", "Souveraine Contributors", "TestUser").
Remove absolute home directory path from tool defs doc comment.
Add souveraine.toml to .gitignore so it won't be re-tracked.

src/core/tools/todo.rs

@@ -719,7 +719,7 @@ mod tests {
             let text = if id == "matrix-1" { "phase one" } else { "phase two" };
             let content = format!(
                 "---\nid: {id}\ntext: {text}\ncreated_at: {created}\nnature: obligation\n\
-                 energy: consumptive\nsource: casey\nmomentum: hot\nstatus: pending\n\
+                 energy: consumptive\nsource: user\nmomentum: hot\nstatus: pending\n\
                  completed: false\nlast_touched: {created}\nthread: \"matrix-sensorium\"\n---\n\n{text}\n"
             );
             std::fs::write(dir.join(format!("{id}.md")), content).unwrap();