Fix color theme issues after git setup

Tmux:
- Add explicit terminal = "screen-256color" to prevent home-manager
  from overriding with plain "screen" terminal setting
- This ensures proper 256-color support for gruvbox theme

Neovim:
- Set explicit colorscheme to maintain consistency with lualine theme
- Remove confusing "no custom colorscheme" comment

Also update flake.lock with latest dependencies.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

flake.lock

@@ -6,11 +6,11 @@
         "nixpkgs": "nixpkgs"
       },
       "locked": {
-        "lastModified": 1752797049,
-        "narHash": "sha256-bc8KceOB9tAl8reHLGRcHfHx1sga0uMCA7koXWQp3A8=",
+        "lastModified": 1753401857,
+        "narHash": "sha256-Oeah0iQYlIV3QXk7f8vaFpQOTg8Nl40g79HMj0qpgfM=",
         "owner": "sadjow",
         "repo": "claude-code-nix",
-        "rev": "ce6b22f6c2b7fa6d24ee1080560909804a33a196",
+        "rev": "4749ca9ab9c13d9aa06525549f9378584f22c181",
         "type": "github"
       },
       "original": {
@@ -44,11 +44,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1752814804,
-        "narHash": "sha256-irfg7lnfEpJY+3Cffkluzp2MTVw1Uq9QGxFp6qadcXI=",
+        "lastModified": 1753470191,
+        "narHash": "sha256-hOUWU5L62G9sm8NxdiLWlLIJZz9H52VuFiDllHdwmVA=",
         "owner": "nix-community",
         "repo": "home-manager",
-        "rev": "d0300c8808e41da81d6edfc202f3d3833c157daf",
+        "rev": "a1817d1c0e5eabe7dfdfe4caa46c94d9d8f3fdb6",
         "type": "github"
       },
       "original": {
@@ -64,11 +64,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1747494142,
-        "narHash": "sha256-7TAUwDVZWq82t/x3+zZ5y+Tjl2hLL2c8+8pv9zCUbTo=",
+        "lastModified": 1751313918,
+        "narHash": "sha256-HsJM3XLa43WpG+665aGEh8iS8AfEwOIQWk3Mke3e7nk=",
         "owner": "nix-darwin",
         "repo": "nix-darwin",
-        "rev": "8e251e45346e9d58e0eece2512e40c183f967e8f",
+        "rev": "e04a388232d9a6ba56967ce5b53a8a6f713cdfcf",
         "type": "github"
       },
       "original": {
@@ -80,11 +80,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1752747119,
-        "narHash": "sha256-2Kp9St3Pbsmu+xMsobLcgzzUxPvZR7alVJWyuk2BAPc=",
+        "lastModified": 1753151930,
+        "narHash": "sha256-XSQy6wRKHhRe//iVY5lS/ZpI/Jn6crWI8fQzl647wCg=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "fa0ef8a6bb1651aa26c939aeb51b5f499e86b0ec",
+        "rev": "83e677f31c84212343f4cc553bab85c2efcad60a",
         "type": "github"
       },
       "original": {
@@ -96,11 +96,11 @@
     },
     "nixpkgs_2": {
       "locked": {
-        "lastModified": 1747426788,
-        "narHash": "sha256-N4cp0asTsJCnRMFZ/k19V9akkxb7J/opG+K+jU57JGc=",
+        "lastModified": 1753399495,
+        "narHash": "sha256-7XG/QBqhrYOyA2houjRTL2NMa7IKZZ/somBqr+Q/6Wo=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "12a55407652e04dcf2309436eb06fef0d3713ef3",
+        "rev": "0d00f23f023b7215b3f1035adb5247c8ec180dbc",
         "type": "github"
       },
       "original": {