feat(db): mesh data model — meshes, members, invites, audit log

- pgSchema "mesh" with 4 tables isolating the peer mesh domain
- Enums: visibility, transport, tier, role
- audit_log is metadata-only (E2E encryption enforced at broker/client)
- Cascade on mesh delete, soft-delete via archivedAt/revokedAt

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.env.example

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+# Since .env is gitignored, you can use .env.example to build a new `.env` file when you clone the repo.
+# Keep this file up-to-date when you add new variables to \`.env\`.
+
+# This file will be committed to version control, so make sure not to have any secrets in it.
+# If you are cloning this repo, create a copy of this file named `.env` and populate it with your secrets.
+
+
+# The database URL is used to connect to your database.
+DATABASE_URL="postgresql://turbostarter:turbostarter@localhost:5432/core"
+
+# The name of the product. This is used in various places across the apps.
+PRODUCT_NAME="TurboStarter"
+
+# The url of the web app. Used mostly to link between apps.
+URL="http://localhost:3000"
+
+# Default locale of the apps, can be overridden separately in each app.
+DEFAULT_LOCALE="en"