chore: add .env support with gitignore protection

[PierreBrisorgueil]

Summary

• Add .env and .env.* to .gitignore to prevent accidental secret commits (.env.example excluded)
• Create .env.example with all DEVKIT_NODE_stripe_* billing variables as documentation
• Update start and dev scripts to use Node 22's --env-file=.env for automatic env loading

Test plan

• .env with real values is NOT tracked by git
• .env.example IS tracked by git
• All 264 unit tests pass
• Manual: npm start loads env vars from .env correctly

Summary by CodeRabbit

• Chores
  • Added an example environment configuration with Stripe Billing placeholders (API keys, webhook signing secret, and pricing IDs) for easy setup.
  • Updated ignore rules to keep real environment/secret files out of version control while retaining the example template.
  • Enabled conditional loading of environment variables during application startup for both production and development runs.

[coderabbitai]

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: eba42fde-0940-4952-b1a5-2356399e1c04

📥 Commits

Reviewing files that changed from the base of the PR and between 2f1de7d and 37b736a.

📒 Files selected for processing (1)

• package.json

Walkthrough

Adds an example environment file with Stripe Billing variable placeholders, updates .gitignore to ignore real env files while keeping the example, and modifies package.json scripts to optionally load .env at runtime via Node's --env-file-if-exists flag.

Changes

Cohort / File(s)	Summary
Environment template & ignore rules .env.example, .gitignore	Adds .env.example with Stripe secret, webhook secret, and multiple price ID placeholders; updates .gitignore to ignore .env* while un-ignoring .env.example.
Runtime script updates package.json	Modifies start and dev scripts to include --env-file-if-exists=.env so Node will load .env when present (keeps previous behavior otherwise).

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• feat(billing): scaffold billing module with Stripe SDK #3248: Billing config changes that consume the DEVKIT_NODE_stripe_* environment variables added by this PR.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 inconclusive)

Check name	Status	Explanation	Resolution
Description check	❓ Inconclusive	The description covers the core summary but lacks most required sections from the template (Scope, full Validation checklist, and Guardrails details).	Complete the Scope section (modules impacted, cross-module impact, risk level), full Validation checklist, and Guardrails section to align with the repository template.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main changes: adding .env support while protecting secrets via gitignore.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[Copilot]

Pull request overview

This PR adds first-class local environment file support while protecting secrets from being committed, and documents the required Stripe billing environment variables.

Changes:

• Update start / dev scripts to load environment variables from .env via Node’s --env-file.
• Add .env / .env.* to .gitignore while explicitly allowing .env.example.
• Add .env.example documenting Stripe billing-related DEVKIT_NODE_* variables.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 1 comment.

File	Description
package.json	Load env vars from .env automatically for start and dev.
.gitignore	Prevent accidental commits of .env files while keeping .env.example tracked.
.env.example	Provide documented placeholders for Stripe billing configuration.

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@package.json`:
- Around line 26-27: The package.json scripts "start" and "dev" hard-fail when
.env is missing because they use --env-file=.env; change both scripts to use
--env-file-if-exists=.env so Node 22 will load the file only if present (i.e.,
update the "start" and "dev" script values to replace --env-file=.env with
--env-file-if-exists=.env).

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: 26e6c83a-5af3-4797-8a55-436f97ccb49c

📥 Commits

Reviewing files that changed from the base of the PR and between 197768c and ce54b72.

📒 Files selected for processing (3)

• .env.example
• .gitignore
• package.json