the 159-hour flake bump lands, nixpkgs moves Jul 5 to Jul 18

Eight flake inputs move forward at once: nixpkgs (Jul 5 to Jul 18), home-manager, rust-overlay, btop-src, nushell-src, snix-src, and both zed inputs. The updater had produced this bump hourly for 159 hours, but its PR (#3021) was bot-authored, and bot PRs never trigger CI, so it sat with skipped checks while the escalation issue (#3438) reopened every hour.

The staleness was not free: ix follows index’s nixpkgs, so the old Jul 5 pin downgraded TigerBeetle under the billing ledger’s one-way-upgraded data file when an unrelated pin bump relocked it (ix#7844). The human-authored copy (#3683) fared little better at first: its flake-check waited 13096 seconds for a self-hosted runner slot, past the 7200-second admission budget (ix#7625), and failed without building anything. The bump itself was pushed to main directly (93ba54768); the nushell-src move needed one follow-up for reedline’s git outputHashes (3fce70541). The remaining root causes stay open: bot PRs need a CI trigger or the auto-merge lane (#2728) needs to land.