directory: hide the clients line at 0, and profile links are logo only

Clients line: a count of 0 (or an absent count) now renders NO line at all —
never "0 clients", never a dash. The >=1 rules (the plural, the plain number)
are unchanged. Same rule in the runtime renderer and in build-directory.py.

Links row: LinkedIn/GitHub/Upwork/Fiverr now render as LOGO ONLY. The four marks
are one uniform monochrome set (Simple Icons v13, 24x24, single-path), inlined so
the row makes no request and each mark inherits currentColor. Self-hosted copies
in static/icons/. Each link keeps its accessible name (aria-label + title, e.g.
"GitHub profile"); the inline SVG is aria-hidden + focusable=false; the hit area
is 36x36 around a 24px mark, with a visible focus ring.

A null/blank link value still renders no anchor (no empty icon).

static/icons/github.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" role="img" aria-label="GitHub"><path fill="currentColor" d="M12 .297c-6.63 0-12 5.373-12 12 0 5.303 3.438 9.8 8.205 11.385.6.113.82-.258.82-.577 0-.285-.01-1.04-.015-2.04-3.338.724-4.042-1.61-4.042-1.61C4.422 18.07 3.633 17.7 3.633 17.7c-1.087-.744.084-.729.084-.729 1.205.084 1.838 1.236 1.838 1.236 1.07 1.835 2.809 1.305 3.495.998.108-.776.417-1.305.76-1.605-2.665-.3-5.466-1.332-5.466-5.93 0-1.31.465-2.38 1.235-3.22-.135-.303-.54-1.523.105-3.176 0 0 1.005-.322 3.3 1.23.96-.267 1.98-.399 3-.405 1.02.006 2.04.138 3 .405 2.28-1.552 3.285-1.23 3.285-1.23.645 1.653.24 2.873.12 3.176.765.84 1.23 1.91 1.23 3.22 0 4.61-2.805 5.625-5.475 5.92.42.36.81 1.096.81 2.22 0 1.606-.015 2.896-.015 3.286 0 .315.21.69.825.57C20.565 22.092 24 17.592 24 12.297c0-6.627-5.373-12-12-12"/></svg>