Initial project setup for PhaseFlow

Set up Next.js 16 project with TypeScript for a training decision app
that integrates menstrual cycle phases with Garmin biometrics for
Hashimoto's thyroiditis management.

Stack: Next.js 16, React 19, Tailwind/shadcn, PocketBase, Drizzle,
Zod, Resend, Vitest, Biome, Lefthook, Nix dev environment.

Includes:
- 7 page routes (dashboard, login, settings, calendar, history, plan)
- 12 API endpoints (garmin, user, cycle, calendar, overrides, cron)
- Core lib utilities (decision engine, cycle phases, nutrition, ICS)
- Type definitions and component scaffolding
- Python script for Garmin token bootstrapping
- Initial unit tests for cycle utilities

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

flake.nix

@@ -0,0 +1,23 @@
+# ABOUTME: Nix flake for PhaseFlow development environment.
+# ABOUTME: Provides Node.js 24, pnpm, turbo, and lefthook.
+{
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  outputs = { nixpkgs, ... }:
+    let
+      system = "x86_64-linux";
+      pkgs = nixpkgs.legacyPackages.${system};
+    in {
+      devShells.${system}.default = pkgs.mkShell {
+        packages = with pkgs; [
+          nodejs_24
+          pnpm
+          turbo
+          lefthook
+        ];
+
+        # For native modules (sharp, better-sqlite3, etc.)
+        LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath [ pkgs.stdenv.cc.cc ];
+      };
+    };
+}