fix: resolve natural language dates when converting filters to Bases

[thaidmfinnick]

Problem

BasesFilterConverter copies natural language date values as plain strings:

Filter	Generated Bases expression	Result
due is today	note.due == "today"	never matches
due is on or before today	note.due <= "today"	string comparison; digits sort before letters, so every date matches, including future ones

The in-memory filter (FilterUtils) resolves these values with resolveNaturalLanguageDate, but the Bases converter never does, so converted saved views behave differently from the original v3 views.

Fix

• Add getNaturalLanguageDateOffsetDays() to dateUtils. It returns the day offset for the same patterns resolveNaturalLanguageDate supports (today, tomorrow, yesterday, next/last week, in N days/weeks, N days/weeks ago).

• In convertOperator, when a date property (due, scheduled, completedDate, dateCreated, dateModified, or a date user field) is compared to a natural language value, emit an expression relative to today(). The comparison uses the date part, like FilterUtils and the default base templates do:

  (!note.due.isEmpty() && date(note.due).format("YYYY-MM-DD") == today().format("YYYY-MM-DD"))
  (!note.due.isEmpty() && date(note.due).format("YYYY-MM-DD") <= (today() + "3 days").format("YYYY-MM-DD"))
  

  The date stays relative, so the generated .base file is still correct on later days.

• Literal dates and non-date properties are unchanged.

Tests

• New tests/unit/services/BasesFilterConverter.naturalLanguageDates.test.ts: 13 of its cases fail before this change.
• npm run test:unit passes, as do eslint and prettier on the changed files and tsc --noEmit.

Video error and demo

Error
https://github.com/user-attachments/assets/6e1a1722-fa61-41e9-8d1e-4cc363777ee0

[thaidmfinnick]

Closing: opened by mistake while investigating a v3 issue that's already fixed in v4.