Update nix flake and plugin version for v0.15.0 (#930)

Release prep for v0.15.0, which ships #907. Bumps nix/package.nix and both plugin.json versions; the v0.15.0 tag goes on this commit.

Author: jeremy

.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "basecamp-cli",
-  "version": "0.14.0",
+  "version": "0.15.0",
   "description": "Basecamp integration for Claude Code. Create todos, track work, link code to projects.",
   "author": {
     "name": "37signals",

.codex-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "basecamp-cli",
-  "version": "0.14.0",
+  "version": "0.15.0",
   "description": "Use Basecamp from Codex to find work, create todos, and keep projects up to date.",
   "author": {
     "name": "37signals",

nix/package.nix

@@ -3,7 +3,7 @@
 buildGoModule.override { go = go_1_26; } (finalAttrs: {
   pname = "basecamp";
   # Updated automatically by scripts/update-nix-flake.sh on each release.
-  version = "0.14.0";
+  version = "0.15.0";
 
   src = lib.cleanSource ./..;