Release v1.5.0

[skitsanos]

Summary

• Bump transcribeit to v1.5.0.
• Add Gemini Files API upload reuse keyed by prepared audio SHA-256.
• Add Gemini explicit cachedContent reuse with TTL controls.
• Normalize explicit Gemini cache telemetry in manifests.
• Split Gemini provider internals into smaller modules.
• Update README and provider/CLI/troubleshooting docs.

Validation

• ./scripts/check.sh
• cargo clippy --all-targets -- -D warnings