docs: split README into a leaner top page + topic docs

[avanelsas]

Summary

The README had grown to 677 lines, with three sections (Recipes,
Adding-a-new-BareDOM-component, Project-layout) taking up two-thirds
of the file. First-time visitors landing on the README for "what
is this" or "how do I run it" had to scroll past almost half of a
long-form walkthrough they didn't ask for.

This PR pulls the deep-dive content into the existing `docs/`
directory (which already houses `architecture.md` and
`plugins.md`) and gives the README a new `## Docs` section
between Features and Authoring shortcuts with one-line pointers to
the four docs.

What moved

From README	To	Lines
Recipes (walkthrough + quick ref)	`docs/recipes.md` (new)	335
Adding a new BareDOM component	`docs/adding-components.md` (new)	75
Project layout	folded into `docs/architecture.md`	36

What stayed

Marketing hook sections — Why Bareforge?, Features, Authoring
shortcuts (the v0.2.0 highlight), Fields & bindings, Templates,
Status, Quick start, Philosophy, Contributing — plus the new
`## Docs` section. README is now 246 lines (down 64%) while
keeping every user-facing top-of-funnel feature mention.

Link integrity

• The walkthrough's `Fields & bindings` link
  rewrites to `../README.md#fields--bindings` so it still
  resolves on GitHub.
• Fixture paths in the walkthrough (e.g.
  `test/fixtures/export/demo-store-with-bindings.json`) gain a
  `../` prefix.
• The Features bullet that pointed at the in-README `#recipes`
  anchor now points at `docs/recipes.md`.
• All four `docs/*.md` links in the new `## Docs` section
  resolve.

Test plan

This is a documentation refactor — no code changes. Standard gates
re-run as muscle memory:

• `cljfmt check` — all source files formatted correctly.
• `npx shadow-cljs compile test` — 571 tests, 0 failures.
• `npx shadow-cljs release app` — 0 warnings under Closure Advanced.
• `clj-kondo --lint src test scripts` — 0 errors, 0 warnings.

Render-side checks worth doing post-merge:

• Open the rendered `README.md` on github.com — `## Docs`
  bullets resolve, all section anchors work.
• Open `docs/recipes.md` — internal step links land, fixture
  paths resolve, the back-link to `../README.md#fields--bindings`
  jumps to the right anchor.
• Open `docs/adding-components.md` — renders cleanly.
• Open `docs/architecture.md` — the appended Project layout
  section sits before "Where to read next".

🤖 Generated with Claude Code