feat: give the chapters motion, diagrams, and retrieval practice

Three strands of work on the chapter surface, all reading from the same
constraint: this site ships no runtime dependencies, so every effect below
is native CSS or an .astro component.

Motion (src/styles/motion.css, DrawRule.astro). A scroll-driven layer of
reveals, hero parallax, section depth, and a hairline that paints itself
along its path, scrubbed by `animation-timeline: view()` — 0KB against
lottie-web's ~60KB gzipped on the main thread. Every scrubbed rule sits
inside `prefers-reduced-motion: no-preference` and `@supports`, so a
Firefox reader or an opted-out one gets the complete static page rather
than one with holes in it. Ranges key to `cover 40%`-`cover 75%` where the
motion is meant to be watched: `view()` ranges key to first visibility,
which on a 2600px page is long before anyone is reading the section.
`.agents/skills/motion/references/scroll-driven.md` records the technique
and the two ways `pathLength` normalisation was broken while building it.

Diagrams (StepFlow.astro, WorktreeMap.astro). The `.steps` stack on
/skills/, /models/, and /agents/ becomes a numbered flow with connectors,
and /agents/ grows the worktree map it was describing in prose — reusing
the `trees` collection rather than a second set of strings. The map's
static variant is gated one class deeper than full-guide's page styles, so
the interactive copy renders byte-identical. Connectors are pseudo-elements,
not SVG: a stretched path desynchronises its own dash pattern, and a
straight line does not need one. Mermaid was considered and rejected at
~1MB of runtime.

Retrieval practice (/rules/, /skills/). A "check yourself" section of
native `<details>` question/answer pairs plus a citation row, both bilingual
through the existing `data-copy` toggle, and both JavaScript-free.

Two audit blind spots surfaced and are closed rather than worked around:
`build.inlineStylesheets: 'never'`, because Astro inlined sheets under ~4kB
and audit-ui.mjs reads its colour and size baseline from dist/_astro/*.css;
and `--columns` declared in the grid components, because an element-level
custom property is not a declaration the audit can resolve.

legacy/styles/skills.css is renamed and imported for its side effect. Inside
a *page*, `?url` resolves to that page's own CSS chunk whatever file it
names, so the link pointed at the wrong asset and the sheet was emitted but
never loaded — the package preview had been rendering unstyled and
overflowing since the Astro cutover.

verify.mjs gains 5 assertions for the recall sections and their Portuguese
copy: 89 now, against the 84 baseline.

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

src/content/chapters/models.json

@@ -1,31 +1,55 @@
 {
   "id": "models",
-  "eyebrow": { "en": "Model routing", "pt": "Model routing" },
-  "title": { "en": "Choose the<br><em>engine.</em>", "pt": "Choose the<br><em>engine.</em>" },
+  "eyebrow": {
+    "en": "Model routing",
+    "pt": "Model routing"
+  },
+  "title": {
+    "en": "Choose the<br><em>engine.</em>",
+    "pt": "Choose the<br><em>engine.</em>"
+  },
   "lede": {
     "en": "A model has a capability ceiling. Effort controls how much room it gets to reason. Route by uncertainty and verification cost.",
     "pt": "A model has a capability ceiling. Effort controls how much room it gets to reason. Route by uncertainty and verification cost."
   },
   "cards": [
     {
-      "label": { "en": "LOW", "pt": "LOW" },
-      "title": { "en": "Bounded rhythm", "pt": "Bounded rhythm" },
+      "label": {
+        "en": "LOW",
+        "pt": "LOW"
+      },
+      "title": {
+        "en": "Bounded rhythm",
+        "pt": "Bounded rhythm"
+      },
       "copy": {
         "en": "Lookup, small edits, formatting, and transformations with clear checks.",
         "pt": "Lookup, small edits, formatting, and transformations with clear checks."
       }
     },
     {
-      "label": { "en": "MEDIUM", "pt": "MEDIUM" },
-      "title": { "en": "Default work", "pt": "Default work" },
+      "label": {
+        "en": "MEDIUM",
+        "pt": "MEDIUM"
+      },
+      "title": {
+        "en": "Default work",
+        "pt": "Default work"
+      },
       "copy": {
         "en": "Normal implementation where the contract is clear but context matters.",
         "pt": "Normal implementation where the contract is clear but context matters."
       }
     },
     {
-      "label": { "en": "HIGH", "pt": "HIGH" },
-      "title": { "en": "Ambiguity", "pt": "Ambiguity" },
+      "label": {
+        "en": "HIGH",
+        "pt": "HIGH"
+      },
+      "title": {
+        "en": "Ambiguity",
+        "pt": "Ambiguity"
+      },
       "copy": {
         "en": "Planning, architecture, security judgment, and hard failures.",
         "pt": "Planning, architecture, security judgment, and hard failures."
@@ -34,37 +58,58 @@
   ],
   "sections": [
     {
-      "eyebrow": { "en": "Two knobs", "pt": "Two knobs" },
-      "title": { "en": "Capability<br>× effort", "pt": "Capability<br>× effort" },
-      "panelLabel": { "en": "ROUTING RULE", "pt": "ROUTING RULE" },
+      "eyebrow": {
+        "en": "Two knobs",
+        "pt": "Two knobs"
+      },
+      "title": {
+        "en": "Capability<br>× effort",
+        "pt": "Capability<br>× effort"
+      },
+      "panelLabel": {
+        "en": "ROUTING RULE",
+        "pt": "ROUTING RULE"
+      },
       "panelCode": {
-        "en": "strong model + high effort → frame ambiguity · light model + low effort → bounded execution · raise one knob at a time → compare evidence",
-        "pt": "strong model + high effort → frame ambiguity · light model + low effort → bounded execution · raise one knob at a time → compare evidence"
+        "en": "strong model + high effort → frame ambiguity\nlight model  + low effort  → bounded execution\nraise one knob at a time   → compare evidence",
+        "pt": "strong model + high effort → frame ambiguity\nlight model  + low effort  → bounded execution\nraise one knob at a time   → compare evidence"
       }
     },
     {
-      "eyebrow": { "en": "Sequence", "pt": "Sequence" },
+      "eyebrow": {
+        "en": "Sequence",
+        "pt": "Sequence"
+      },
       "title": {
         "en": "Spend judgment<br>where it <em>compounds.</em>",
         "pt": "Spend judgment<br>where it <em>compounds.</em>"
       },
       "steps": [
         {
-          "label": { "en": "Plan", "pt": "Plan" },
+          "label": {
+            "en": "Plan",
+            "pt": "Plan"
+          },
           "copy": {
             "en": "Strong model: scope, risks, acceptance, and worktree split.",
             "pt": "Strong model: scope, risks, acceptance, and worktree split."
           }
         },
         {
-          "label": { "en": "Build", "pt": "Build" },
+          "label": {
+            "en": "Build",
+            "pt": "Build"
+          },
           "copy": {
             "en": "Focused worker: smallest context and lightest model that can pass.",
             "pt": "Focused worker: smallest context and lightest model that can pass."
           }
         },
         {
-          "label": { "en": "Review", "pt": "Review" },
+          "label": {
+            "en": "Review",
+            "pt": "Review"
+          },
           "copy": {
             "en": "Independent pass when missed issues cost more than the call.",
             "pt": "Independent pass when missed issues cost more than the call."