feat(marketing): phase 4 — the marketing pages

PLAN.md §13 phase 4: /features/, /architecture/, /modules/, /integrations/, and
/community/ — plus the two scope items the phase table never assigned to anyone.

Six decisions taken by the org lead before coding, recorded in PLAN.md §10 as
D20-D25:

- D20 /features/ is the homepage's list with a `detail` line, not a second list.
  One data file, two renderings, so they cannot disagree about what exists.
- D21 /architecture/ draws reasons, not reference: three new inline SVGs, one per
  boundary. No endpoint tables, no config keys — those are phase 8's and stay
  canonical in docs/.
- D22 The deliberate absences of §2 become one tagged data file, rendered on the
  three pages that promise them.
- D23 Phase 4 absorbs /community/ (specified in §10 and §14 N3, linked from the
  header since phase 1, built by no phase) and checkLinks.mjs.
- D24 `needsModule`: writing the Teams detail exposed a false claim phase 3
  shipped. Teams are module-sourced only — teams.module_id is NOT NULL, there is
  no create route, sync is gated on providerModuleId() — so the Community group
  no longer says a bare core does all of it.
- D25 The per-capability demo affordance brand.json had promised since phase 2 is
  a deep link, filled at boot from data-demo-path.

checkLinks.mjs reads the built HTML rather than src/, because half these links
are assembled from data files and template literals. Its PLANNED_ROUTES list is
checked in both directions, so it cannot rot into a permanent exemption.

applyBrand.mjs gained a pass that recomputes deep links from their immutable
path, making it idempotent and reversible; checkBrand.mjs lifts that pattern out
and runs it against the stock markup so the two cannot drift. Both proved
against a real mount, in both directions.

Fixes a cascade bug the checks could not see: [data-demo-url=''] and a scoped
component class are both specificity 0,1,0, so .demo-link's `display` beat the
hide rule and twelve links to a nonexistent demo rendered, each resolving to the
current page. The rule is now !important.

The four diagrams' shared SVG vocabulary moved to src/styles/diagram.css.

Verified from a clean checkout: npm ci, all five checks, astro check (0 errors),
production build, and a live browser pass at desktop and 390px.

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

src/components/home/DataPath.astro

@@ -159,12 +159,6 @@ import platform from '../../data/platform.json';
     top: calc(var(--header-h) + 1.5rem);
   }
 
-  .flow {
-    display: block;
-    width: 100%;
-    max-width: 380px;
-  }
-
   .datapath__caption {
     margin: 1rem 0 0;
     max-width: 380px;
@@ -172,75 +166,14 @@ import platform from '../../data/platform.json';
     font-size: 0.85rem;
   }
 
-  /* ---- The drawing ------------------------------------------------------
-     SVG presentation attributes cannot take a var(), so every colour here is
-     set as a CSS property on a class instead. That is also what keeps
-     checkTokens.mjs satisfied: no literal reaches the markup. */
-  .node {
-    fill: var(--panel-b);
-    stroke: var(--line);
-    stroke-width: 1;
-  }
+  /* The SVG vocabulary this diagram draws with -- .node, .spine, .arrow,
+     .boundary, .rings -- now lives in src/styles/diagram.css, shared with
+     /architecture/'s three. It was duplicated in four files the moment the
+     second diagram existed, and the rules it holds are decisions about what a
+     diagram on this site looks like rather than about this one.
 
-  .node--self {
-    fill: var(--panel-a);
-    stroke: var(--gold-deep);
-  }
-
-  .node-title {
-    fill: var(--head);
-    font-family: var(--sans);
-    font-size: 17px;
-    font-weight: 600;
-  }
-
-  .node-sub {
-    fill: var(--dim);
-    font-family: var(--sans);
-    font-size: 12.5px;
-  }
-
-  .spine {
-    fill: none;
-    stroke: var(--gold-deep);
-    stroke-width: 2;
-  }
-
-  .spine--live {
-    stroke: var(--portal);
-    filter: drop-shadow(0 0 6px var(--portal-deep));
-  }
-
-  .arrow {
-    fill: var(--gold-deep);
-    stroke: none;
-  }
-
-  .arrow--live {
-    fill: var(--portal);
-  }
-
-  .boundary {
-    fill: none;
-    stroke: var(--line);
-    stroke-width: 1;
-    stroke-dasharray: 4 5;
-  }
-
-  .boundary-label {
-    fill: var(--dim);
-    font-family: var(--sans);
-    font-size: 11px;
-    letter-spacing: 0.09em;
-    text-transform: uppercase;
-  }
-
-  .rings {
-    fill: none;
-    stroke: var(--gold-deep);
-    stroke-width: 1;
-    opacity: 0.16;
-  }
+     The layout below stays here: the right-hand column is a numbered walk,
+     not the notes column .diagram__body assumes. */
 
   /* ---- The list ---------------------------------------------------------- */
   .datapath__steps {