logo: revert artwork to source orientation (was over-flipped)

Source PNG from the MPS lumbda-logos product is already an inverted λ
(hooks at top-left + bottom-right, V-body). My prior commit applied
vertical + horizontal flips on top of that, which undid the inversion
and produced a right-side-up calligraphic λ — the opposite of what
the artwork was drawn to express.

Regenerate both PNG variants (lumbda-logo.png black,
lumbda-logo-green.png #227842) directly from the source with no
flips. Only transform: alpha-from-brightness so anti-aliased edges
survive over any background.

Homepage img src picks up ?v=2 so any browser with the flipped
version in disk cache re-fetches. Logo size stays 3.33× the
wordmark font (10.66rem). PDF + HTML rebuilt — embed-images.py
base64-inlines the new PNG into the HTML automatically.

www/index.html

@@ -12,7 +12,7 @@
 
 <header>
   <h1 aria-label="lumbda.">lumbda<span class="period" aria-hidden="true">.</span></h1>
-  <img class="lambda-mark" src="lumbda-logo-green.png" alt="" aria-hidden="true">
+  <img class="lambda-mark" src="lumbda-logo-green.png?v=2" alt="" aria-hidden="true">
   <p class="tagline">feedback as a primitive</p>
 </header>
 

www/style.css

@@ -53,16 +53,15 @@ header {
   margin-bottom: 2rem;
 }
 
-/* Brand mark — custom λ artwork (pre-flipped both axes at bake time,
+/* Brand mark — custom upside-down λ artwork, recolored to #227842
-   recolored to #227842 with proper alpha). Shipped as a PNG so PDF,
+   with proper alpha from pixel brightness. Shipped as a PNG so PDF,
-   print, and any print-styled email renders it consistently instead
+   print, and print-styled email all render consistently without
-   of depending on CSS transforms. Sized 3× the wordmark font so it
+   relying on CSS transforms. Sized 3.33× the wordmark font. */
-   carries the page. */
 header .lambda-mark {
   display: block;
-  width: 9.6rem;         /* 3× the 3.2rem h1 font-size */
+  width: 10.66rem;       /* 3.33× the 3.2rem h1 font-size */
   height: auto;
-  margin: 0.4rem 0 0.6rem;
+  margin: 0 0 0.6rem;    /* sit flush against the wordmark's descender */
 }
 
 header h1 {