Iteration 1: file-backed projects with auto-named temps, lock file, and L1 CLI

Replaces the in-memory database with an on-disk project. Startup either
opens a project at the positional CLI path (L1) or creates an auto-named
temp project (<YYYYMMDD>-<word>-<word>-<word>) under the OS-standard
data directory or a --data-dir override. The new project::Project type
owns the directory skeleton and a PID+hostname lock file with
stale-lock takeover via sysinfo. The status bar now shows
"Project: <Display Name>", derived by a small kebab/snake/camel
prettifier. Per-command persistence to YAML/CSV/history.log is NOT
yet wired -- that's Iteration 2; for now playground.db carries the
state across quits.

Tests: 257 passing (231 lib + 9 new integration + 17 existing),
0 failing, 0 skipped. Clippy clean with nursery lints.

src/main.rs

@@ -25,7 +25,7 @@ fn main() -> ExitCode {
         }
     };
 
-    match tokio_rt.block_on(runtime::run(args.theme)) {
+    match tokio_rt.block_on(runtime::run(args)) {
         Ok(()) => ExitCode::SUCCESS,
         Err(e) => {
             tracing::error!(error = %e, "runtime exited with error");