release: v1.4.1 — security & stability patch

Security: lock down the TutorBot tool sandbox (shell exec is opt-in, all
filesystem/shell access confined to the bot workspace) and isolate per-user
resources, closing #518, #517, #516, #515, #514 and #506 (first hardened in
#507).

Bug fixes: chat input disabled after the first turn (#520), KB embedding
failure on long documents (#521 / #509), profile creation under Docker
(#512 / #513), Qwen reasoning models failing native tool calling (#527 / #528),
the GPT-5 init-wizard token parameter (#508), and oversized session-event
truncation (#524).

Features: HTTP/SSE API for multi-turn chat with a specific TutorBot (#511),
multimodal image fallback for vision-capable providers without a capability
entry, safe ZIP knowledge upload, and a /settings/network page with model
fetching (community PRs #522 and #523 reimplemented locally).

Also bumps __version__ to 1.4.1, adds the v1.4.1 release notes, updates the
README Releases section, and ships the Astro + Starlight docs site under site/.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>