fix: mitigate hash collision risk by using full SHA256 hash

[echobt]

Problem

The previous implementation used only the first 8 bytes (64 bits) of the SHA256 hash for generating project database filenames. This limited the hash space significantly, increasing the risk of collisions via the birthday paradox as the number of projects grows. A collision would result in two different projects sharing the same database file, leading to data corruption.

Solution

This PR changes the hash_path function in src/config.rs to use the full SHA256 hash (32 bytes / 64 hex characters) instead of truncating it. This effectively eliminates the risk of accidental collision for all practical purposes.

Testing

• Verified that hash_path now returns a 64-character hex string.
• Ran existing tests with cargo test to ensure no regressions.