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

.gitignore

@@ -37,11 +37,10 @@ pkg/spec/dist/
 # goreleaser local output
 /dist/
 
-# inspect web bundle output (real bundle wired in Stage 4 via Makefile/CI).
-# Track only the stub index.html + .gitkeep so //go:embed succeeds.
+# inspect web bundle output; built by `make web-build` before go build.
+# Only .gitkeep is tracked so //go:embed all:dist compiles on a fresh checkout.
 /internal/inspect/dist/*
 !/internal/inspect/dist/.gitkeep
-!/internal/inspect/dist/index.html
 
 # inspect web frontend
 inspect-ui/node_modules/
@@ -53,15 +52,9 @@ examples/folio-web/node_modules/
 examples/folio-web/dist/
 examples/folio-web/.vite/
 
-# d2 diagrams render into build/site/_assets/diagrams; keep sources only
-/docs/_diagrams/*.svg
-/docs/_diagrams/*.png
-
 # coding agent files
 .claude/
 .claude/*
 
 # Personal research notes
 /research/
-
-internal/inspect/dist/*