docs(#2077): drop impl-history provenance from runner.rs module doc

'Mirrors the logic previously embedded in hive-ag3nt' is pure provenance
(where the code moved from) — the #2077 rubric says drop impl-history. The
rest of my slice (nix modules + hive-priv/matrix-mcp/bash-mcp + forge.rs) is
already lean: surveyed it, the long comment blocks are all legit why/invariant/
contract docs under the 30-line threshold, not bloat.

hive-bash-mcp/src/runner.rs

@@ -1,6 +1,6 @@
 //! Bash subprocess runner: spawns `bash -c <cmd>` tasks, writes status
 //! files under `harness/bash-tasks/`, and fires hyperhive wake signals
-//! on completion. Mirrors the logic previously embedded in `hive-ag3nt`.
+//! on completion.
 //!
 //! Files under `tasks_dir()`:
 //! - `<id>.json`  — task metadata + status (pending → running → done)