Fixes identified from testing emcli email search (Morphy Richards purchase investigation).

1. No folder discovery command

emcli has no folders command, so the agent cannot enumerate available mailboxes. Searches default to INBOX only and miss archived mail (e.g. INBOX.Archive).

Fix: Add a folders agent command to list available mailboxes.

2. INBOX-only default too narrow

When searching for a specific email, the agent should ideally search across all folders, but cannot without knowing folder names.

Fix: Add an --all-folders flag to search to sweep all mailboxes at once.

3. --text full-text search unreliable on some IMAP servers

On myfamilyemail.co.uk, --text returned zero results for emails that --subject-contains found fine. The IMAP server either does not support full-text search or has an incomplete index.

Fix: Document this limitation in the skill; recommend --subject-contains as the primary search method and treat --text as best-effort.

4. No way to distinguish filtered vs missing vs wrong-folder

All three cases return empty results with no error, making it impossible for the agent to know whether mail is absent, hidden by a whitelist, or simply in another folder.

Fix: emcli (or the skill) should surface a diagnostic hint when results are empty — e.g. suggest running folders or retrying with --all-folders.