fix(headless): correct default dictionary backup path

[dvd233]

Description

Fixes #2431.

LocalFileConfig prepends the directory containing hanlp.properties to both default dictionary paths. The backup default started with ./data, which produced conf./data/dictionary/backup after string concatenation. Align the backup default with the latest dictionary default so the packaged path is conf/data/dictionary/backup.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature
• Breaking change
• This change requires a documentation update

How Has This Been Tested?

• git diff --check passed.
• Added LocalFileConfigTest to lock the corrected default value.
• Maven tests could not be run locally because this environment does not have JDK 21 or Maven installed; repository CI should provide the runtime verification.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas (no new complex logic)
• I have made corresponding changes to the documentation (not required for this bug fix)
• I have added a regression test for the fix
• New and existing unit tests pass locally (Maven unavailable in the local environment)