drop the stale stable-pin rationale

Two nixpkgs pins are unremarkable and the version-specific reason rots; the flake and AGENTS no longer carry it.

AGENTS.md

@@ -60,5 +60,4 @@ Everything comes from the Nix flake devshell; do not install toolchains by hand.
 - The CI image provides `nix-ld`, `jq`, `sqlite`, `node`, `zstd` and a `runner` user that `cache-nix-action` expects. None of that is needed locally beyond the devshell.
 - Integration servers: navidrome on 4533 (`admin`/`password`), gonic on 4747 (`admin`/`admin`), lms on 5082 (`admin`/`subtracks-lms`), Nextcloud Music on 8090 (`admin`/`subtracks-nextcloud`, base URL `http://localhost:8090/index.php/apps/music/subsonic/`). The test music is cached in `.integration/music` (gitignored).
 - lms and Nextcloud Music authenticate the Subsonic API with per-user **API keys** instead of passwords. The harness seeds a key and most tests use `useTokenAuth = false`; `SubsonicAuthIntegrationTest` drives `useTokenAuth = true` and asserts the fallback to plaintext (lms answers code 42, Nextcloud 41).
-- The integration shell takes its server packages from a pinned stable nixpkgs (`nixpkgs-stable`), because lms 3.80 in nixpkgs-unstable segfaults at startup with wt 4.14.3.
 - `nix develop` does not source your shell rc files (so tools like atuin are not active); use direnv if you want your normal interactive shell.

flake.nix

@@ -3,7 +3,6 @@
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
-    # lms 3.80 (unstable) segfaults at startup with wt 4.14.3; stable ships a working 3.78.
     nixpkgs-stable.url = "github:NixOS/nixpkgs/nixos-26.05";
   };