fix(nix): give the macOS build the toolchain of the other platforms

The first darwin build of the root flake failed in komorebi-workspace-deps:
rustc 1.92.0 is not supported by sysinfo@0.39.6 (requires rustc 1.95).
rust-toolchain.toml says channel = stable, and kfm-rust-overlay was pinned
to 1d3f83ba (January 2026), whose stable is 1.92.0, while the unified lock
now has sysinfo 0.39/0.40 and parking_lot 0.13 (rust-version 1.95, the
highest in the macOS and the KDE closures by cargo metadata).

kfm-rust-overlay (flake.nix, flake.lock, and the pin in
komorebi-for-mac/flake.lock) now uses 19ecdd08, the revision the root
flake's own rust-overlay and kfde-rust-overlay lock; its stable is 1.99.1.
kfm-nixpkgs and every other input are unchanged.

Verified (nix eval of drvPath, throwaway git copy before/after): the
Windows deps, clippy and nextest, and the kfde deps, clippy, nextest and
VM suite stacks are identical; kfm deny, fmt and toml-fmt change (the
toolchain). rust-bin.stable.latest version evaluated: 1.99.1 at the new
rev, 1.92.0 at the old one. Not verified: the darwin clippy, nextest and
deps drvPaths cannot be evaluated on this Linux host (the stub source is a
derivation the host cannot build); no build run.

flake.lock

@@ -401,17 +401,17 @@
         ]
       },
       "locked": {
-        "lastModified": 1767581716,
-        "narHash": "sha256-FUbiUzdrGkLou37OGfb4vCLPnqdSIvtmJBxjh2iljiE=",
+        "lastModified": 1793174968,
+        "narHash": "sha256-u5nUf4cewaT36iIzG1s/VECktqUMiZaGF5BsgervsvQ=",
         "owner": "oxalica",
         "repo": "rust-overlay",
-        "rev": "1d3f83babdd21e16bf5cfe0f1efcb4f49ee1bc2c",
+        "rev": "19ecdd08213836b36c4296a3a4f4af5a3d5308db",
         "type": "github"
       },
       "original": {
         "owner": "oxalica",
         "repo": "rust-overlay",
-        "rev": "1d3f83babdd21e16bf5cfe0f1efcb4f49ee1bc2c",
+        "rev": "19ecdd08213836b36c4296a3a4f4af5a3d5308db",
         "type": "github"
       }
     },

flake.nix

@@ -41,7 +41,7 @@
     kfm-flake-parts.url = "github:hercules-ci/flake-parts/a34fae9c08a15ad73f295041fec82323541400a9";
     kfm-flake-parts.inputs.nixpkgs-lib.follows = "kfm-nixpkgs-lib";
     kfm-crane.url = "github:ipetkov/crane/7d59256814085fd9666a2ae3e774dc5ee216b630";
-    kfm-rust-overlay.url = "github:oxalica/rust-overlay/1d3f83babdd21e16bf5cfe0f1efcb4f49ee1bc2c";
+    kfm-rust-overlay.url = "github:oxalica/rust-overlay/19ecdd08213836b36c4296a3a4f4af5a3d5308db";
     kfm-rust-overlay.inputs.nixpkgs.follows = "kfm-nixpkgs";
     kfm-treefmt-nix.url = "github:numtide/treefmt-nix/d56486eb9493ad9c4777c65932618e9c2d0468fc";
     kfm-treefmt-nix.inputs.nixpkgs.follows = "kfm-nixpkgs";

komorebi-for-mac/flake.lock

@@ -140,11 +140,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1767581716,
-        "narHash": "sha256-FUbiUzdrGkLou37OGfb4vCLPnqdSIvtmJBxjh2iljiE=",
+        "lastModified": 1793174968,
+        "narHash": "sha256-u5nUf4cewaT36iIzG1s/VECktqUMiZaGF5BsgervsvQ=",
         "owner": "oxalica",
         "repo": "rust-overlay",
-        "rev": "1d3f83babdd21e16bf5cfe0f1efcb4f49ee1bc2c",
+        "rev": "19ecdd08213836b36c4296a3a4f4af5a3d5308db",
         "type": "github"
       },
       "original": {