v1.7.0

fix(ui): eliminate remaining unrenderable glyphs + add glyph guardrail

A new test-only glyph_guard scans src string literals for glyphs outside the
app's bundled fonts (arrows, Greek, box-drawing, geometric shapes, dingbats,
angle quotes) and fails — it immediately found more than the manual sweeps:
Greek μ/σ in stats labels (deep_learning, main, service_monitor, ml_lab,
services, export), a second ✓ in the Python compat list, and the correlation
and breadcrumb separators. Converted μ/σ to mean/sd, ✓ to a Phosphor check,
and the separators to ASCII; aligned the paired report/UI tests. Documents the
rule in CONTRIBUTING.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>