chore(maestro): drop obsolete web/dist/.gitkeep handling

build.rs now builds web/dist before include_dir! evaluates, so the
checked-in .gitkeep placeholder is no longer needed for a fresh checkout
to compile (verified by building with web/dist entirely absent). Ignore
dist/ wholesale and update the static_bundle doc comment.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/maestro-web/src/static_bundle.rs

@@ -1,10 +1,11 @@
 //! Embedded `web/dist` SPA bundle.
 //!
-//! The build of `web/` is consumed at compile time via `include_dir!`. The
-//! macro requires the directory to exist; an empty `web/dist/.gitkeep` is
-//! checked in so a fresh checkout compiles without first running `pnpm build`.
-//! The resulting binary just serves a 404 for `/` until the operator runs the
-//! frontend build (see top-level `Justfile`'s `web` target).
+//! The build of `web/` is consumed at compile time via `include_dir!`, which
+//! requires the directory to exist. `build.rs` runs `pnpm build` before the
+//! crate compiles, so `web/dist` is always present and populated — even on a
+//! fresh checkout (`web/dist` is gitignored and never committed). The
+//! placeholder below is therefore defensive only; a successful build always
+//! embeds the real bundle.
 
 use axum::body::Body;
 use axum::http::{header, StatusCode};