fix: preserve tags in property-based identification (#1391)

[normenmueller]

fix-task-prop-based-ident

Property-based task identification preserves tags

This change prevents property-based identification from mutating tags automatically. Tags are only written when the user explicitly sets them (including default tags), while the identifying property is still applied.

Examples (illustrative):

• Creating a task with property identification and tags like client, urgent keeps those tags; no extra task tag is injected.
• Updating priority/status without touching tags leaves existing tags unchanged.

Changelog

Task Identification

• Only add the identifying task tag to frontmatter when tag-based identification is enabled.
• In property-based mode, preserve user/default tags without filtering them out.
• Only write frontmatter.tags during updates when tags are explicitly provided; otherwise leave tags untouched.
• Fixes [Bug]: Task identification by property does not identify the tasks correctly #1391.

Cf. PR.md