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/06-media-pipeline.svg

@@ -0,0 +1,92 @@
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+<title id="ttl">Media pipeline</title>
+<desc id="dsc">Five stages from download to library: fingerprinting gives every file a natural key so re-runs converge, audit verifies the copy, and review is a deliberate human gate before anything is published.</desc>
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+  <text x="24" y="40" class="big">Media pipeline — download, identify, verify, review, publish</text>
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+  <text x="291.0" y="136.0" class="hd" text-anchor="middle">fingerprint</text>
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+  <text x="861.0" y="136.0" class="hd" text-anchor="middle">library</text>
+  <text x="861.0" y="154.0" class="sub" text-anchor="middle">publish + serve</text>
+  <text x="861" y="168" class="cap" text-anchor="middle">stage 5</text>
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+  <text x="228" y="262" class="hd">Gate, not a queue</text>
+  <text x="228" y="284" class="sub">a file that fails fingerprint or audit</text>
+  <text x="228" y="304" class="sub">stops where a person can see it</text>
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+  <text x="604" y="262" class="hd">Idempotent by identity</text>
+  <text x="604" y="284" class="sub">the fingerprint is the natural key, so a</text>
+  <text x="604" y="304" class="sub">re-run converges instead of duplicating</text>
+  <rect x="24" y="356" width="912" height="92" rx="7" class="node "/>
+  <text x="38" y="382" class="hd">The same shape at 10 files and at 10,000</text>
+  <text x="38" y="404" class="sub">every stage is a separate step with its own failure mode, so a bad stage can be re-run alone</text>
+  <text x="38" y="426" class="sub">the review stage is deliberately manual: automating it would move the risk, not remove it</text>
+  <text x="24" y="480" class="sub">Encoding, thumbnailing and fingerprinting at scale, with a human gate before anything is published.</text>
+</svg>