v1.1.0 - Configurable cache TTL

What's new

• Add PDB_CACHE_TTL to control how long local PDB files remain fresh.
• Default cache TTL is 1h.
• Set PDB_CACHE_TTL=0 to cache files forever.
• Support Go duration values such as 30m, 1h, and 24h.
• Refresh expired files from the upstream symbol server.
• Continue serving the existing stale cache when an upstream refresh fails.
• Download refreshes to a temporary file before replacing the cached file.
• Stream cached files directly so refreshed content is available immediately.
• Add deployment examples for Docker Compose and the Linux install script.

Verification

• go test ./...
• go test -race ./...
• go vet ./...
• Cross-compiled for Linux amd64/arm64, Windows amd64, and macOS amd64/arm64.