docs: add .env.example for non-Docker local development (#663)

Adds the .env.example file referenced by CONTRIBUTING.md, with the five
required core vars from lib/init.ts plus commented optional extension vars.
Un-ignores it in .gitignore with a !.env.example negation.

Refs #564.

Signed-off-by: Oscar Holm <oscar@numbery.se>

.env.example

@@ -0,0 +1,27 @@
+# Local development environment variables.
+# Copy to .env and fill in the values: cp .env.example .env
+
+# ── Required ──────────────────────────────────────────────
+# Supabase project credentials (Dashboard -> Settings -> API)
+NEXT_PUBLIC_SUPABASE_URL=https://your-project.supabase.co
+NEXT_PUBLIC_SUPABASE_ANON_KEY=your-anon-or-publishable-key
+SUPABASE_SERVICE_ROLE_KEY=your-service-role-or-secret-key
+
+# App base URL (local dev)
+NEXT_PUBLIC_APP_URL=http://localhost:3000
+
+# Secret for authenticating cron/scheduled requests.
+# Any non-empty random string for local dev: openssl rand -hex 16
+CRON_SECRET=generate-a-random-secret
+
+# ── Optional: extension features (core runs without these) ─
+# AI features
+# ANTHROPIC_API_KEY=
+# OPENAI_API_KEY=
+# Bank connections (Enable Banking)
+# ENABLE_BANKING_APP_ID=
+# ENABLE_BANKING_PRIVATE_KEY=
+# Accounting integrations
+# FORTNOX_CLIENT_ID=
+# FORTNOX_CLIENT_SECRET=
+# FORTNOX_REDIRECT_URI=

.gitignore

@@ -33,6 +33,7 @@ yarn-error.log*
 
 # env files (can opt-in for committing if needed)
 .env*
+!.env.example
 
 # vercel
 .vercel
@@ -70,4 +71,4 @@ supabase/.branches/
 /scripts
 
 # Local-only SIE test fixtures — may contain real/scrubbed company data, never commit
-tests/fixtures/sie/
+tests/fixtures/sie/