support block height for reminders and delete

[pory-gone]

Description

fix #1668

• Added block-height support for bot commands:
  • @remindme in N blocks and @remindme at block X
  • @delete in N blocks and @delete at block X

Files changed

• item.js: extended parsing and time calculation in getRemindAt/getDeleteAt for “block(s)” and “at block X”.
• item.js: performBotBehavior now passes current block height (via LND) when available.

Screenshots

N/A

Additional Context

• “at block X” requires LND. Without it, absolute block scheduling is skipped.
• If X ≤ current height, execution is immediate.
• @delete does not produce notifications (soft-delete only); @remindme produces a “Reminder” notification.
• “in N blocks” ≈ N × 10 minutes
• “at block X” uses current chain height from LND; if unavailable, the absolute form is ignored (time/relative forms still work)
• “Last directive wins” behavior preserved.
• No DB schema or API changes; uses existing reminder and deleteItem jobs.

Checklist

Are your changes backward compatible?
Yes.

On a scale of 1–10, how well and how have you QA’d this?
7/10

For frontend changes: tested on mobile, light and dark mode?
NaN

Did you introduce any new environment variables?
NaN

Did you use AI for this? If so, how much did it assist you?

I used AI to understand the context and do research to find the best implementation

[ekzyis]

Hello, I recently updated our PR template to add a question about AI in #2507.

I updated your PR description to include it, see the end of the checklist.

Can you please answer it? Thank you!