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/linkedin.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" role="img" aria-label="LinkedIn"><path fill="currentColor" d="M20.447 20.452h-3.554v-5.569c0-1.328-.027-3.037-1.852-3.037-1.853 0-2.136 1.445-2.136 2.939v5.667H9.351V9h3.414v1.561h.046c.477-.9 1.637-1.85 3.37-1.85 3.601 0 4.267 2.37 4.267 5.455v6.286zM5.337 7.433c-1.144 0-2.063-.926-2.063-2.065 0-1.138.92-2.063 2.063-2.063 1.14 0 2.064.925 2.064 2.063 0 1.139-.925 2.065-2.064 2.065zm1.782 13.019H3.555V9h3.564v11.452zM22.225 0H1.771C.792 0 0 .774 0 1.729v20.542C0 23.227.792 24 1.771 24h20.451C23.2 24 24 23.227 24 22.271V1.729C24 .774 23.2 0 22.222 0h.003z"/></svg>