feat: eReader email labels + AnythingLLM integration

[allencai222]

Summary

This PR introduces two independent UX improvements for Calibre-Web users:

1. eReader email label support + send to specific address

Problem: Users with multiple Kindle/eReader email addresses configured (comma-separated in their profile) cannot choose which device to send a book to — it always sends to all addresses simultaneously.

Changes:

• cps/helper.py: valid_email() now accepts Name <email> entries alongside plain addresses. A new extract_email() helper extracts the bare address from either format.
• cps/templates/user_edit.html: Input type changed from email to text; label updated to explain the Name <email> syntax.
• cps/web.py (send_to_ereader): Reads a email POST parameter and validates it against the current user's own address list before sending to that single address.
• cps/templates/detail.html: Dropdown items show Format → Label (using the configured label/name, falling back to the raw address). Each item passes the bare address via data-email.
• cps/static/js/details.js: AJAX POST now includes the selected email field.

Backward compatibility: Existing plain-address entries continue to work without changes. The fallback for missing/invalid email POST param is the first configured address.

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2. AnythingLLM integration

Problem: There is no built-in way to push books from Calibre-Web into a local AI knowledge base.

Changes:

• cps/config_sql.py: Two new config fields — config_anythingllm_url and config_anythingllm_api_key.
• cps/admin.py: Persists the two new fields via _config_string.
• cps/templates/config_edit.html: Admin UI — enable checkbox + server URL + API key inputs (collapsed when disabled, styled consistently with the Goodreads section).
• cps/web.py (send_to_anythingllm): POST route that uploads the book file (EPUB or PDF) to AnythingLLM's document API, then embeds it into a per-book workspace named calibre-{title} (auto-created if absent).
• cps/templates/detail.html: "Send to AnythingLLM" button rendered only when the integration is configured, for books that have an EPUB or PDF.
• cps/static/js/details.js: Click handler with spinner/disabled state during the (potentially slow) embedding request.

No external dependencies: Uses Python's standard urllib.request only.

Test plan

• Profile page: enter My Kindle <user@kindle.com>, Backup <other@kindle.com> — save succeeds, plain addresses also still accepted
• Book detail: single email → button shows label; multiple emails → dropdown lists Format → Label per entry; clicking sends only to that address
• Admin config: AnythingLLM section visible, saves URL + key, section hidden when unchecked
• Book detail with AnythingLLM configured: "Send to AnythingLLM" button appears for EPUB/PDF; absent when integration disabled
• AnythingLLM button: spinner shown during request; success/error flash message displayed

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