[PianoNic]

Summary

• search keeps query and gains terms (OR'd synonyms, up to 8), from/to (modified or received date) and sources (files, channels, mail, chats, pages). One call fans out over all terms and sources in parallel (4 at a time, 25 s overall timeout) and returns one merged list.
• OneNote page titles are searched too (same endpoint as search_pages), only with OneNote read.
• Hits are deduplicated per item and ranked by title match, number of terms matched, the rank the source gave them, then recency. Each hit carries source, title, snippet, author, modified date, location label, link, matchedTerms, readWith and the ids the read tools need.
• The answer lists searched and skipped sources (with the missing permission) and sets partial when a source failed, timed out or has more results than were fetched. Mail needs Mail read, chats and channels need Teams read, OneNote needs OneNote read.
• Date filtering is applied to the returned hits, not through KQL, because the plugin's per-drive fallback and OneNote search do not understand KQL. Hits without a date are kept.
• Helply's prompt now tells it to search once with all word variants and a date range, with the single-source tools as fallback.

Closes #602