Prevent DuckDB token disclosure

[hjosugi]

Summary

• read ICEBERG_TOKEN with DuckDB getenv() instead of embedding its value in generated SQL
• update bash, zsh, and PowerShell setup guidance
• bump the project to v1.0.1 and verify all version declarations agree
• reject release tags that do not match VERSION

Root cause

The SQL generator interpolated Settings.token into a CREATE SECRET statement. Redirecting the documented command therefore wrote the R2 API token to disk, and entering equivalent SQL directly could expose it through DuckDB CLI history.

DuckDB 1.3 added expression support in CREATE SECRET; this project requires DuckDB 1.4+, so getenv('ICEBERG_TOKEN') is available.

Security impact

Generated SQL and release examples no longer contain the configured R2 token. The credential exists only in the DuckDB process environment and in DuckDB's temporary in-memory secret.

Validation

• pytest: 8 passed
• ruff check .: passed
• generated SQL contains getenv('ICEBERG_TOKEN') and not a sentinel token
• v1.0.1 release ZIP built successfully
• git diff --check: passed

Closes #2