feat(models): gate optional models behind required mistral+nomic-embed

Models page redesign: tabs (Required/Recommended/Installed) with a
multi-column card grid, required models (memory curator + embeddings)
surfaced first and gating the rest until both are installed. Adds a
qwen2.5:14b tier to the hardware-fit catalog for high-VRAM machines.
Installer and restore messaging updated to match. Also declares pytest
in requirements-base.txt so bin/check.sh's test suite is reproducible
on a fresh venv.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

requirements-base.txt

@@ -45,6 +45,8 @@ python-docx
 sqlite-vec
 # Local speech-to-text: CTranslate2-based, no torch, keeps dictation on-device.
 faster-whisper
+# Email client: IMAP read (SMTP send is stdlib). Pure-Python, no native deps.
+imap-tools
 
 # Documentation Support
 markdown-it-py
@@ -52,3 +54,6 @@ MarkupSafe
 mdurl
 Pygments
 Jinja2
+
+# Testing (bin/check.sh is the release gate; it shells out to pytest)
+pytest