fix: Format dates as YYYY-MM-DD in ft md exports instead of using raw string slice

[ccage-simp]

Description

In v1.3.2, the new ft md command generates markdown files using a simple string slice on the postedAt or bookmarkedAt database field: date.slice(0, 10).

While this works for standard ISO string timestamps (2024-11-27), it fundamentally breaks for any user whose database still contains bookmarks in the legacy Twitter date format (Fri Apr 01 16:02:20 +0000 2022).

For legacy timestamps, slicing the first 10 characters yields Fri Apr 01. This results in markdown exports with filenames like Fri Apr 01-author-slug.md which:

1. Cannot be sorted chronologically by the filesystem.
2. Are missing the year entirely.
3. Contain spaces, making them harder to script against.

The Fix

This PR replaces the raw string slice with a robust Date parser in src/md-export.ts. It parses whatever timestamp format exists in the database and explicitly constructs a uniform, sortable YYYY-MM-DD prefix for every exported file.

[MrDwarf7]

Related #69

[afar1]

reviewing

[ccage-simp]

Closing. Being considered in #53.

[ccage-simp]

Reopened. Apologies @afar1 if I confused things related to issue #53 and your plan to address this.

[afar1]

Thanks for surfacing and patching this. The merged fix in #104 covers the markdown date regression end-to-end, including the broader export path we needed, so I’m closing this one as superseded.