docs: document the changes since 1.2.0 and add the DevTools page

[dangreen]

Why

The site and the READMEs describe the 1.2.0 release, while main already carries the breaking changes of the next one: tasks on signals (#222, #223), static operators (#260), the SignalsMap classes (#261), the DevTools panel (#263) and the development builds (#236). The docs were kept on the released API on purpose; this PR brings them to what the next release ships.

What

• Tasks (feat(kida,store,query)!: attach tasks to the signals they fill #222, feat(kida)!: attach the resolved promise as a task and hand values through verbatim #223): task($signal, ...) and waitTasks($signal) replace TasksRunner$, the pool and waitCurrentTasks in the store core concepts, SSR and testing pages, the query SSR and testing pages and the tutorial. hydratable() is the whole SSR setting of a query client, so the ssr and tasks sections are gone.
• resolved (feat(kida)!: attach the resolved promise as a task and hand values through verbatim #223): falsy values are data, and its promise is a task.
• SignalsMap (feat(store,query)!: replace the signals map functions with the SignalsMap and IndexedSignalsMap classes #261): the section is rewritten for SignalsMap and IndexedSignalsMap.
• Operators (feat(kida,store)!: return a plain result from the operators when every operand is static #260, 505d947): static operands give plain values, pick and text get their sections, concat is removed.
• New helpers: latest (feat(kida): add latest for the value of the source that changed last #231), child in the kida README (feat(kida): export child to build custom child signals #250), toHtmlAttribute (fix(router,ssr): render the httpEquiv meta prop as the http-equiv attribute #253), escapeHtml in the adapter example (fix(ssr,react-ssr,preact-ssr,svelte-ssr): escape head values and the dehydrated snapshot in the rendered html #239), parseLocales with null (fix(platform-web): accept null in parseLocales for a missing Accept-Language header #244).
• DevTools (feat(devtools,store): add the DevTools panel #263): a page in the Store section after Testing, with the development builds and the warnings they print (feat: add development diagnostics with separate development and production builds #236, fix(agera): drop the development warning about a signal written inside a computed #266). The package is listed on the getting-started page, the landing and the root README, and its README links to the page.
• Numbers: the benchmark and bundle size tables come from docs(website): add the comparison page #235, measured on 2026-09-27 with Node.js 26.10.0.
• Fixes on the way: the store README Quick Start called onMount on a signal that is not mountable, stale samples in the agera and kida READMEs, pager labels that pointed at the wrong pages after Agent Skills and the store integrations were added, the StackBlitz file of the CV example.
• skills/*/DOCS.md are regenerated with pnpm skills:docs.

Notes

• docs(website): add the comparison page #235 (the comparison page) is stacked on this branch.
• Checked: astro check, astro build, pnpm skills:docs --check, and the internal links and anchors between the pages: the only new broken one is /query/ssr#ssr in the April article, left as it was written.
• deferEffect and inspect are not documented: deferred scopes have been off the site since 5b15d22, and inspect is a contract of the devtools that may change in minor versions.
• The SSR table of the Rick and Morty example predates docs: move the rick-and-morty query keys out of the store factories and use hydratable() in the shared stores #270, which grew the client JS of react-nano_kit-ssr by 44 B raw and 65 B gzip.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.24%. Comparing base (cdf1238) to head (ebe2e3b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #271   +/-   ##
=======================================
  Coverage   83.24%   83.24%           
=======================================
  Files         228      228           
  Lines        4835     4835           
  Branches     1071     1071           
=======================================
  Hits         4025     4025           
  Misses        574      574           
  Partials      236      236           

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