docs: clarify search_emails scope, point to advanced_search

[AusDavo]

Summary

• Updated search_emails tool description from the vague "Search emails by subject or content" to explicitly state it only does full-text body/subject search, and directs users to advanced_search for field-specific filtering (sender, recipient, date, etc.)
• Updated the query parameter description from "Search query string" to "Text to search for in email body and subject lines"

Problem

AI clients (Claude, etc.) consistently misuse search_emails by passing structured queries like from:user@example.com or sender names, expecting it to filter by sender. The tool silently returns zero results because JMAP's text filter only matches body/subject content. The client then has to fall back to get_recent_emails and scan manually.

The advanced_search tool already supports from, to, subject, and date parameters — but nothing in search_emails tells the client it exists or that search_emails can't do field-specific filtering.

Fix

Two description changes in the tool definition (no logic changes):

1. Tool description: "Full-text search of email body and subject. Does not filter by sender, recipient, or date — use advanced_search for field-specific filtering."
2. Query param description: "Text to search for in email body and subject lines"

Test plan

• npm run build passes cleanly
• Verify AI clients select advanced_search instead of search_emails when filtering by sender/recipient

🤖 Generated with Claude Code

[MadLlama25]

Thanks @AusDavo — the description clarification is a genuinely good catch and it's now on main (adapted with attribution). Closing this PR rather than merging because it had grown beyond the docs scope (Dockerfile, docker-compose, an HTTP transport rewrite) and had conflicts with main. If you'd like to propose the Docker/HTTP-transport work, a fresh focused PR for each would be very welcome.