refactor(gui): slot system standard — single register, four props shares, framework store seat

The definitive slot model for the web client, replacing the first-generation
define/register two-step, ScopedSlots whitelist faces, and binding handles:

- 'root' is the only a-priori slot (SlotsService built-in); the shell renders
  exactly ctx.slots.renderSlot('root', {}).
- register is the single API: children = slot declaration + render
  authorization + runtime spec in one options object; misconfiguration fails
  loud at load (duplicate declaration, undeclared contribution, one store
  handle under two scopes).
- Component props arrive in four auto-derived shares: PropsRuntime<K>
  (owner params + session/global standard kits via declare-merge),
  PropsRenderSlots<S>, PropsStore<H>, and the inject business face.
  sessionId is framework-supplied; hooks are framework-made only.
- Framework store seat: defineStore factories declare schema/actions/persist;
  read = useStore, write = baked actions only; store scope derives from the
  mounting entry; per-session persist keys and clearPersisted lifecycle.
- inject factories read the apply closure's own ctx (binding handles retired;
  root-ctx back door closed); SessionProvider is self-wired render-prop.
- Rendering sits behind the SlotRenderer install seam; runtime stays
  React-free; ownership ledger keyed to the single entry axis closes the
  stale-authority window (StaleAuthorizationError probes).

Docs: the slot type-chain note is refreshed in place as the slot system
standard RFC (bilingual pair re-recorded); the web client architecture RFC
defers its slot sections there; packages/client/AGENTS.md gains the slot and
props discipline; gui-testing/web-styling notes drop missions/ references.

Tests: suites rewritten to the standard (props fed directly, real store
engines via createXXXStore().create(), no render machinery); load-time
negative samples for declaration/authorization/store conflicts; verified by
real-host playwright run (three columns, empty state, collapse, keyed session
remount, cross-slot selection sharing).

docs(ui-sidebar): point contract reference at the committed slot standard RFC

missions/ is workspace-local and never committed; the README must not cite it.

.agents/notes/implemented/process/2026-07-19-web-styling-system.md

@@ -2,7 +2,7 @@
 
 Status: implemented
 
-> Token-system update (2026-07-22): the framework rulings here (CSS Modules + clsx, no component library, no tailwind, tokens-only colors) remain in force, but the two-layer `--bg-*`/`--text-*` token table and its `web-ui/src/style/global.css` home were replaced by the `--dsw-*` static+alias sheets in `packages/client/ui-theme/src/styles/` (dark = `body[data-ds-dark-theme]` override). Current authority: `missions/tasks/20260721-1520-web-plugin-rfc/architecture.md` §15.
+> Token-system update (2026-07-22): the framework rulings here (CSS Modules + clsx, no component library, no tailwind, tokens-only colors) remain in force, but the two-layer `--bg-*`/`--text-*` token table and its `web-ui/src/style/global.css` home were replaced by the `--dsw-*` static+alias sheets in `packages/client/ui-theme/src/styles/` (dark = `body[data-ds-dark-theme]` override) — the sheets themselves are the token authority.
 
 English | [中文](2026-07-19-web-styling-system.zh.md)