feat(dank): enable DMS/niri session on mibook, pin HM to release-26.05, drop redundant keybinds

- Pin home-manager input to release-26.05 to match nixpkgs (was resolving
  to HM master / 26.11, causing a Home Manager version mismatch warning).
- Drop niri.enableKeybinds = true from the dank HM config; keybinds are
  already provided by the imported DMS niri homeModule (includes), and using
  both together triggered the "enableKeybinds and includes.enable" warning.
- Enable my.profiles.dank on mibook (machines/mibook/environments.nix).
- Rebuild confirmed exit 0 with both target warnings resolved.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018Sv2QAunLcLo3tS1YsfLgN

flake.lock

@@ -138,15 +138,16 @@
         ]
       },
       "locked": {
-        "lastModified": 1784877405,
-        "narHash": "sha256-W649GocILahx7Vb/JMx834217+OLKBrq014VmC/8+NM=",
+        "lastModified": 1784350909,
+        "narHash": "sha256-ZWyzLbS1yKUTeFJLmdVuWNnHttL333/ldJbEE+KzCrM=",
         "owner": "nix-community",
         "repo": "home-manager",
-        "rev": "32de400b6ac9f43042bca706f4a64f6ad08117e8",
+        "rev": "4ce190229c73d44536caa7072f6308fb2d8feeb3",
         "type": "github"
       },
       "original": {
         "owner": "nix-community",
+        "ref": "release-26.05",
         "repo": "home-manager",
         "type": "github"
       }