test(make-pdf): width-policy unit suite + landscape e2e gate with negative fixtures

24 unit tests weighted toward the false-positive guards: wide screenshot
without an alt hint stays portrait, sub-threshold and tall images stay
portrait, deterministic 1560/1561px boundary, whole-word alt matching
('photographic' must not match 'graph'), page=portrait veto beats every
heuristic, diagnostic blocks never promote. E2E gate asserts pdfinfo
per-page boxes through the compiled binary: exactly 3 of 5 fixture blocks
get landscape pages (alt-hinted image, directive-forced image, wide sequence
diagram) while the unhinted screenshot and the veto'd diagram stay portrait —
plus the --toc combo proving TOC and named-page landscape coexist.

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

make-pdf/test/fixtures/landscape-gate.md

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+# Landscape Gate
+
+Intro text under the first heading.
+
+## Negative: screenshot stays portrait
+
+![just a screenshot of the app](./diagram-assets/wide-screenshot.png)
+
+## Positive: alt-hinted wide image promotes
+
+![architecture diagram of the system](./diagram-assets/wide-arch.png)
+
+## Positive: directive forces a small image
+
+![small forced](./diagram-assets/red-box.png){page=landscape}
+
+## Positive: wide diagram auto-promotes
+
+```mermaid title="Wide sequence"
+sequenceDiagram
+  participant A as seqalpha
+  participant B as seqbeta
+  participant C as seqgamma
+  participant D as seqdelta
+  participant E as seqepsilon
+  participant F as seqzeta
+  participant G as seqeta
+  participant H as seqtheta
+  participant I as seqiota
+  participant J as seqkappa
+  A->>J: long hop
+  B->>I: cross
+```
+
+## Negative: directive vetoes a wide diagram
+
+```mermaid page=portrait
+sequenceDiagram
+  participant A as vetoalpha
+  participant B as vetobeta
+  participant C as vetogamma
+  participant D as vetodelta
+  participant E as vetoepsilon
+  participant F as vetozeta
+  participant G as vetoeta
+  participant H as vetotheta
+  participant I as vetoiota
+  participant J as vetokappa
+  A->>J: long hop
+```
+
+Closing text.