project_scan should detect warehouse credentials in .env files

**Current behavior:** `project_scan` discovers warehouse connections from `connections.json`, dbt `profiles.yml`, Docker containers, and well-known environment variables (e.g., `DATABASE_URL`, `PGHOST`). However, it does not check for `.env` files in the project directory, which are a very common place to store connection details — especially in migration and multi-warehouse projects.

**What happened:** A `.env` file in the project root contained Fabric server and database credentials (`FABRIC_SERVER`, `FABRIC_WAREHOUSE_DB`, `FABRIC_LAKEHOUSE_DB`) that were missed during the initial environment scan. These had to be found manually afterward.

**Suggested improvement:** `project_scan` should parse `.env` and `.env.*` files in the project root for connection-related variables. Even if the variable names are non-standard, the tool could surface them as "potential warehouse credentials found in .env" and let the user confirm. The `.env.example` file could also be used as a hint for expected variable names.

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### Metadata

| Field | Value |
|-------|-------|
| CLI Version | 0.7.0 |
| Platform | darwin |
| Architecture | arm64 |
| OS Release | 24.3.0 |
| Category | improvement |
| Working Directory | microsoft-fabric |
| Session ID | ses_20d3e0f8cffetVBGsWpBSJq7hu |