Phase 7: authored assets (diagrams, code exhibits, client wall, budget)

Phase 7 is mostly authored assets. This commit is the asset half; the
template half is a Builder child issue because this phase must not write
application code.

DoD items satisfied or advanced:

- [x] Eight diagrams present, both themes, readable at 1x and on mobile
      8 SVGs, one byte-identical <style> block across all 8 (one visual
      language by construction). Light and dark resolve from a single file
      via prefers-color-scheme, verified per file in Chrome: 8/8 return two
      distinct palettes. Geometry verified with getBBox(), not estimated:
      0 findings after fixing 74 (text overflow, partial overlap, empty
      text, out-of-viewBox). Mobile type at the 900px minimum is 14.1/12.2px.

- [x] Six code exhibits with a two-sentence rationale each
      212 verbatim lines across five eras, copied with cp/sed from the
      read-only archive. Every rationale is exactly two sentences about why
      the code is good; every exhibit also carries an honest_note, and where
      the code is not good the note says so (the 3,400-line procedural PHP
      script is presented for its operational judgement, not its structure).

- [~] Every image optimised; total page weight budgeted and recorded
      BUDGET.md records measured raw and gzip weights for all 15 served
      files: 63,802 B raw / 13,220 B gzipped. Zero rasters by design. Page
      weight of a real page is not measurable until Phase 2 templates and
      Phase 3 serving exist, and is recorded as open rather than asserted.

- [x] Archive never linked or exposed
      No mount paths or volume names under content/. Provenance recorded as
      "private archive, path withheld".

- [ ] Client wall reads as deliberate  -> needs markup/CSS (Builder)
- [ ] Lighthouse held at >= 95/95      -> needs a served page (Phase 3)

Also: the client wall is authored as data (45 entries, 44 distinct names) with
the 45-vs-46 discrepancy and the Diajio -> Diageo correction recorded
rather than papered over. No commercial marks are enabled: that is a
permission decision for Sam, so availability is recorded and permission is not
implied.

content/assets/diagrams/08-era-timeline.svg

@@ -0,0 +1,106 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 960 540" width="960" height="540" role="img" aria-labelledby="ttl dsc">
+<title id="ttl">Era timeline</title>
+<desc id="dsc">Five consecutive platform eras from Flash and ActionScript through jQuery and PHP, React and TypeScript, server-driven Go with HTMX, to agent systems, on an axis from 2000 to 2026. Era boundaries are approximate; the bands show order.</desc>
+<style>
+    text{font-family:ui-sans-serif,-apple-system,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;fill:#1b222b;font-size:15px}
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+    .zone{fill:none;stroke:#aab4c0;stroke-width:1.4;stroke-dasharray:7 6}
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+    .mA{fill:#1a6bc4}
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+    .mW{fill:#b45309}
+    .dot{fill:#6b7684}
+    .tick{stroke:#aab4c0;stroke-width:1.2}
+  @media (prefers-color-scheme: dark){
+    text{fill:#e7edf4}
+    .sub,.cap{fill:#98a4b3}
+    .node{fill:#182028;stroke:#35424f}
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+  }
+</style>
+<defs>
+  <marker id="aN" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path class="mN" d="M0,0 L10,5 L0,10 z"/></marker>
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+</defs>
+  <text x="24" y="40" class="big">Twenty-five years, five platform shifts</text>
+  <rect x="28" y="96" width="176" height="118" rx="7" class="node"/>
+  <text x="42" y="126" class="cap">01</text>
+  <text x="42" y="144" class="hd">Flash / ActionScript</text>
+  <text x="42" y="168" class="sub">classes, imports,</text>
+  <text x="42" y="186" class="sub">encapsulation</text>
+  <text x="42" y="212" class="sub">client wall</text>
+  <path d="M205,155 L211,155" class="ln"/>
+  <rect x="212" y="96" width="176" height="118" rx="7" class="node"/>
+  <text x="226" y="126" class="cap">02</text>
+  <text x="226" y="144" class="hd">jQuery + PHP</text>
+  <text x="226" y="168" class="sub">media pipelines,</text>
+  <text x="226" y="186" class="sub">FFmpeg, ImageMagick</text>
+  <text x="226" y="212" class="sub">delivery at scale</text>
+  <path d="M389,155 L395,155" class="ln"/>
+  <rect x="396" y="96" width="176" height="118" rx="7" class="node"/>
+  <text x="410" y="126" class="cap">03</text>
+  <text x="410" y="144" class="hd">React + TypeScript</text>
+  <text x="410" y="168" class="sub">typed service</text>
+  <text x="410" y="186" class="sub">layers, tRPC</text>
+  <text x="410" y="212" class="sub">typed front ends</text>
+  <path d="M573,155 L579,155" class="ln"/>
+  <rect x="580" y="96" width="176" height="118" rx="7" class="node node-a"/>
+  <text x="594" y="126" class="cap">04</text>
+  <text x="594" y="144" class="hd">Server-driven</text>
+  <text x="594" y="168" class="sub">Go + templ + HTMX,</text>
+  <text x="594" y="186" class="sub">SQLite</text>
+  <text x="594" y="212" class="sub">this site</text>
+  <path d="M757,155 L763,155" class="ln"/>
+  <rect x="764" y="96" width="176" height="118" rx="7" class="node node-t"/>
+  <text x="778" y="126" class="cap">05</text>
+  <text x="778" y="144" class="hd">Agent systems</text>
+  <text x="778" y="168" class="sub">harnesses, routing,</text>
+  <text x="778" y="186" class="sub">retrieval</text>
+  <text x="778" y="212" class="sub">AI estate</text>
+  <path d="M28,268 L932,268" class="ln"/>
+  <path d="M28,262 L28,274" class="tick"/>
+  <text x="28" y="292" class="hd" text-anchor="start">2000</text>
+  <path d="M546,262 L546,274" class="tick"/>
+  <text x="546" y="292" class="hd" text-anchor="middle">2020</text>
+  <path d="M932,262 L932,274" class="tick"/>
+  <text x="932" y="292" class="hd" text-anchor="end">2026</text>
+  <text x="28" y="314" class="sub">employed delivery</text>
+  <text x="546" y="314" class="sub">independent engineering practice</text>
+  <text x="932" y="314" class="sub" text-anchor="end">now</text>
+  <rect x="28" y="348" width="904" height="118" rx="7" class="node "/>
+  <text x="42" y="376" class="hd">What the five eras have in common</text>
+  <text x="42" y="400" class="sub">· every era was learned by shipping with it, not by reading about it</text>
+  <text x="42" y="424" class="sub">· the artefacts survive: a Flash class, an easing engine, a media pipeline, a typed service layer, a 33-line derivation</text>
+  <text x="42" y="448" class="sub">· the current era is the first where platform, agents and edge hardware are one system</text>
+  <text x="28" y="500" class="sub">Era boundaries are approximate: employed 2000–2020 per the résumé, independent practice 2020–.</text>
+  <text x="932" y="500" class="sub" text-anchor="end">six code exhibits span eras 1–5</text>
+</svg>