feat(docs/product): add university datasheet and GDS-textured header bars

Adds a second audience-specific config alongside the individual product
sheet, plus several fixes to the shared template and build.

datasheet-universities.yaml: written for a department buying for a cohort
rather than an individual. Leads on per-student cost with a worked class
example, carries testimonials from Murmann and Pretl, and answers the
procurement and academic-calendar questions an individual buyer never asks.
US institution list, education@tinytapeout.com as the contact.

Template gains optional quote band, footer contact block, and conditional
eyebrow / doc ref / photo caption so both sheets share one template. The
hero photo now derives its height from the text column instead of a fixed
44mm, so the two columns always end level whatever the copy length.

Header bars carry the chip-layout texture from the tt-datasheet-artwork
repo, renormalised from its native ~7% alpha and rebuilt as black traces:
they darken the bar, so contrast with the white type goes up rather than
down. Bar colour moves from #040371 to THEME_SKY_BLUE #0c66ab, where the
texture is actually legible; the config key is renamed navy -> brand to
match.

Font subset rebuilt from the full Archivo to include U+03A9 — page 2 has
used "< 500 Ω" since the first build and was silently falling back to a
system face. build.py now warns about any character the embedded font
cannot draw, and validates HTML in the config for unbalanced tags and
malformed hrefs, both of which had shipped unnoticed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/product/datasheet.yaml

@@ -31,11 +31,11 @@ doc:
 
 # Colours and the two page-level type sizes. Everything else scales from these.
 theme:
-  navy: "#040371"            # header bars and table header rows
+  brand: "#0c66ab"           # header bars and table header rows
   red: "#ec3013"             # accent: labels, rules, prices
   # DATASHEET tag in the header bar. Official Tiny Tapeout brand colours:
   #   yellow #fef244 · cyan #3dfef7 · hot pink #f82381 · pink #fc9f9f · blue #040371
-  # Set tag_fg to navy for the light colours, #ffffff for hot pink.
+  # Set tag_fg to a dark colour for the light tags, #ffffff for hot pink.
   tag_bg: "#fef244"
   tag_fg: "#040371"
   ink: "#141414"             # body text
@@ -44,6 +44,11 @@ theme:
   ground: "#f2f1f4"          # zebra stripe on tables
   rule: "#c9c8d0"            # thin rules
   rule_hard: "#141414"       # 2px section rules
+  # Chip-layout texture over the header bars, from the tt-datasheet-artwork repo.
+  # Blank the filename for flat bars; raise/lower the opacity for more or
+  # less texture (0.35 subtle, 0.55 balanced, 0.75 strong).
+  bar_texture: bar-texture.png
+  bar_texture_opacity: 0.55
   heading_size: 30pt         # page 1 headline
   body_size: 8.3pt           # feature and FAQ body text
 
@@ -99,8 +104,8 @@ features:
   - kicker: 04 · Process
     title: Three PDKs
     body: >-
-      SkyWater SKY130, IHP sg13g2 and GlobalFoundries gf180mcu. Open-source PDKs
-      running multiple times per year with no NDAs to sign.
+      SkyWater SKY130, IHP sg13g2 and GlobalFoundries gf180mcu. Open-source PDKs,
+      10+ shuttles per year, no NDAs to sign.
   - kicker: 05 · Hardware
     title: Demoboard available
     body: >-
@@ -109,8 +114,9 @@ features:
   - kicker: 06 · Flexibility
     title: Bring your own flow
     body: >-
-      Harden with the supplied open-source LibreLane flow, or use your own tools
-      entirely — the minimum submission is GDS + LEF.
+      Harden with the supplied open-source LibreLane flow, or use any tools you
+      like — commercial or open source — as long as the resulting GDS and LEF
+      can be published.
 
 pricing:
   heading: Pricing
@@ -130,7 +136,7 @@ pricing:
        "Optional add-on: packaged chip on an RP2350 powered demoboard.",
        "€300"]
     - ["Postage & packing",
-       "Flat rate worldwide, charged once per order.",
+       "Flat rate worldwide, charged once per demoboard.",
        "€15"]
   footnote: >-
     <b>The €385 headline is one tile (€70) plus a demoboard (€300) plus postage
@@ -272,7 +278,7 @@ ordering:
     - {}
   rows:
     - ["Shuttle cadence",
-       "Several shuttles per year across the three processes. Check <a href=\"https://app.tinytapeout.com/chips\">tinytapeout.com/chips</a> for the schedule."]
+       "10+ shuttles per year across the three processes. Check <a href=\"https://app.tinytapeout.com/chips\">tinytapeout.com/chips</a> for the schedule."]
     - ["Lead time",
        "6–9 months in fabrication, then assembly, test and fulfilment."]
     - ["Volume discount",
@@ -280,9 +286,9 @@ ordering:
     - ["Deliverable",
        "Silicon area only for remote or shared test, or area plus the demoboard kit: packaged chip, RP2350 demoboard and breakout board."]
     - ["Design tools",
-       "Supplied open-source LibreLane flow running in GitHub Actions, or any toolchain of your own."]
+       "Supplied open-source LibreLane flow running in GitHub Actions, or any commercial or open-source toolchain of your own."]
     - ["Minimum submission",
-       "GDS + LEF in a public repository, licensed Apache-2.0."]
+       "GDS + LEF, produced with any tools, in a public repository under Apache-2.0. Your tools must permit publishing them."]
 
 disclaimer:
   label: Disclaimer