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/code/README.md

@@ -0,0 +1,48 @@
+# Phase 7.3 — code exhibits
+
+Six excerpts, **212 lines**, spanning five eras. Evidence that the range behind
+the claims is real, in a form an engineer can read in two minutes.
+
+## The rules these follow
+
+1. **Verbatim.** Every file is a byte-for-byte copy from the private archive.
+   Nothing is retyped, reformatted or tidied. A retyped excerpt proves nothing.
+2. **Never linked.** The archive is not referenced, linked or served from the
+   public site. Provenance is recorded as "private archive" and the path is
+   withheld from this repository so it cannot leak into a page or a build.
+3. **Two sentences on why it is good code.** `rationale` in `manifest.yaml`.
+   Not what the code does — that is what reading it is for.
+4. **Honest notes.** Where the code is not good, `honest_note` says so. A 2012
+   procedural PHP script presented as elegant would undermine every other claim
+   on the site.
+
+## The six
+
+| # | Era | Language | Lines | What it demonstrates |
+|---|---|---|---|---|
+| 1 | Flash / ActionScript | AS3 | 36 | class, imports, encapsulation |
+| 2 | jQuery + PHP | JavaScript | 42 | easing + timeline core |
+| 3 | jQuery + PHP | PHP | 27 | one encode op + the FFmpeg piping |
+| 4 | React + TypeScript | TypeScript | 37 | types, interfaces, service layer |
+| 5 | Embedded C++ | C++ | 28 | interface split from implementation |
+| 6 | Declarative infrastructure | Nix | 33 | a patch with its own removal condition |
+
+Era 6 is the most modern and the least common. A short, correct, self-documenting
+derivation that says when to delete itself is a better infrastructure signal than
+a thousand lines of configuration.
+
+## Renderer requirements
+
+- Syntax highlighting happens **server-side** (chroma), on the server, at build
+  time. The client receives highlighted HTML. No browser-side highlighter.
+- Line numbers are generated by the template, not embedded in the files.
+- Files stay in `content/assets/code/` as plain text. They are not inlined into
+  a Go string, so the archive copy and the served copy cannot diverge silently.
+- Total weight: 7 KB of source, which compresses well because it is code.
+
+## Honest notes worth reading twice
+
+- Exhibit 1 contains a latent typo, kept.
+- Exhibit 3 is 27 lines out of a 3,400-line file, with one marked elision.
+- Exhibit 4 shows the router rather than the schema it types against.
+- Exhibit 5 is two files presented as one, because the point is the split.