docs: web platform + clean URLs + dark/light mode (#37)

* chore(docs): replace d2 diagram pipeline with mermaid

Remove docs/_diagrams/ and d2 build step from Makefile. The HTML
template already initialises mermaid.js; diagrams are now inline
code fences rendered client-side.

* docs(architecture): add mermaid diagram + web/CDP platform docs

Replace SVG img tag with inline mermaid flowchart showing both native
(Maestro sidecar + in-app SDK) and web (Chrome CDP) paths. Update
Processes, Transports table, and per-step cycle sections.

* docs(design-principles): update principles 1-4 for web platform

Principles 1, 2, 3, and 4 referenced Maestro and native-only concepts.
Add web/CDP context and update driver-is-an-interface to name both
sidecar and chrome implementations.

* docs(manual): add web prerequisites and folio-web example

Update --platform flag to list android, ios, web. Add web prerequisites
section (Chrome, no SDK needed) and folio-web quick-start to
getting-started.

* chore(gitignore): untrack inspect dist/index.html build artifact

index.html is regenerated by vite on every build with a new content hash,
making it permanently dirty. Only .gitkeep is needed for //go:embed to
compile on a fresh checkout. Also remove duplicate dist/* line and stale
d2 diagram ignore entries.

* feat(docs): click-to-zoom for mermaid diagrams

* docs(architecture): change diagram layout from LR to TB

* docs(getting-started): link npm and Maven Central package headers

* update docs root

* docs(spec): rewrite npm package README

Update usage example to current API, drop stale version-compatibility
and license sections.

* build(docs): output pages as pagename/index.html for clean URLs

Split DOCS_OUT into INDEX_OUT (index.md files stay as index.html) and
PAGE_OUT (all other pages become pagename/index.html). The __ROOT__
depth computation already handles the extra directory level correctly.

* chore(docs): update sidebar links to directory-style URLs

* docs: update cross-links from .html to directory-style paths

* ci(docs): remove d2 install step

* feat(docs): dark/light mode toggle

Add theme toggle button (top-right, fixed). Persists preference in
localStorage; falls back to prefers-color-scheme. Flash-free via inline
script in <head> that sets data-theme before first paint.

* fix(docs): fix inspect image path broken by directory URL restructure

* feat(docs): click-to-fullscreen for all article images

* fix(inspect): allow AssetsFS override in ServerOptions; drop unused request param from serveIndex

* fix(inspect): use in-memory FS in tests so TestAssets_FallbackToIndexHTML passes without web build

pkg/spec/README.md

@@ -1,8 +1,8 @@
 # @sanderling/spec
 
-TypeScript spec API for [sanderling](https://github.com/priyanshujain/sanderling), a property-based UI fuzzer for mobile apps.
+TypeScript spec API for [sanderling](https://github.com/priyanshujain/sanderling), a property-based UI fuzzer for mobile and web apps.
 
-Spec authors write specs in TypeScript that describe what an app should *always* do (safety invariants), generate weighted actions to exercise the app, and extract structured state from the accessibility tree. The `sanderling` CLI picks up the spec and drives the app under test.
+Spec authors write properties (what the app must always or eventually do), extractors (structured state from the UI), and action generators (what sanderling is allowed to do). The `sanderling` CLI evaluates the spec in a loop against a running app.
 
 ## Install
 
@@ -13,27 +13,29 @@ npm install --save-dev @sanderling/spec
 ## Usage
 
 ```ts
-import { extract, always, actions, Tap, weighted } from "@sanderling/spec";
+import { extract, always, eventually, now, actions, weighted, taps, swipes, InputText, Tap } from "@sanderling/spec";
 
-export const spec = {
-  extract: extract((tree) => ({
-    onHomeScreen: tree.some((n) => n.text === "Home"),
-  })),
+const loggedIn = extract((s) => !!s.ax.find("id:home-tab-bar"));
+const balance = extract<number>((s) => (s.snapshots.balance as number) ?? 0);
 
-  always: always(({ state }) => state.onHomeScreen || !state.startedOnHome),
-
-  actions: actions(({ tree }) =>
-    weighted([
-      [1, Tap(tree.first((n) => n.text === "Checkout"))],
-    ]),
-  ),
+export const properties = {
+  balanceNeverNegative: always(() => balance.current >= 0),
+  loginSucceeds: eventually(() => loggedIn.current).within(30, "seconds"),
 };
+
+const doLogin = actions(() => {
+  if (loggedIn.current) return [];
+  const email = state.ax.find("id:email-field");
+  const submit = state.ax.find("id:sign-in-button");
+  if (!email || !submit) return [];
+  return [InputText({ into: email, text: "[email protected]" }), Tap({ on: submit })];
+});
+
+export const actions = weighted(
+  [50, doLogin],
+  [10, taps],
+  [2,  swipes],
+);
 ```
 
-## Version compatibility
-
-`@sanderling/spec` is released in lockstep with the sanderling CLI. Pin the same major/minor version as your installed `sanderling` binary.
-
-## License
-
-Apache-2.0
+Works identically across Android, iOS, and web targets.