fix: title auto-generation + mobile close button (PR #333) + v0.50.10

[nesquena-hermes]

Summary

Picks up PR #333 from ccqqlo (title auto-generation fix + mobile close button) and
adds 11 tests covering both changes.

Changes

api/streaming.py — title auto-generation now fires for 'Untitled', 'New Chat', and empty string titles.
Previously only 'Untitled' was covered; sessions arriving from external forks/clients with 'New Chat' as their
default title would never get an auto-generated title after the first message.

static/style.css — On viewports ≤900px, both the desktop collapse button (#btnCollapseWorkspacePanel) and
the mobile X button (.mobile-close-btn) were rendered simultaneously.
Desktop default now hides .mobile-close-btn; the 900px media query shows it and hides the desktop button.

Tests added

tests/test_sprint41.py — 11 tests:

• Title condition covers 'Untitled', 'New Chat', not s.title, and OR logic
• CSS: .mobile-close-btn hidden by default, shown in 900px query
• CSS: #btnCollapseWorkspacePanel hidden in 900px query, existing rules preserved
• HTML: both buttons present with proper aria-label

QA

• 800/802 tests pass (2 pre-existing failures on master; not introduced by this PR)
• Full browser API sanity: 20/20 checks pass
• 11 new tests all pass on PR branch, 6 correctly fail on master

Closes #333