fix(tracking): honor disabled collection

[Agistaris]

Summary

• Honor tracking.enabled = false and RTK_TRACK=0 before opening the history database on normal, passthrough, parse-failure, and consented-telemetry paths.
• Preserve the existing enabled-by-default behavior when configuration cannot be loaded.
• Add a disposable binary regression covering configuration disablement, environment override, parse failure, and the enabled control.

Test plan

• cargo fmt --all -- --check
• cargo clippy --all-targets
• cargo test --test tracking_disabled_test
• Complete Cargo test matrix

The focused binary regression passes 1/1. Disabled cases create no history.db; the enabled control creates it normally. The complete Cargo matrix accounts for 2,584 tests: 2,576 passed, 8 ignored, and 0 failed.

[CLAassistant]

All committers have signed the CLA.