Unify connect.ts onto the host-context model (or remove it if unused)

[mgoldsborough]

Background

PR #6 unified the SDK's host-context handling around a single currentHostContext: McpUiHostContext source of truth in createSynapse. New public API: synapse.getHostContext() / onHostContextChanged() and React useHostContext<T>(). getTheme / useTheme / onThemeChanged are typed selectors over it.

src/connect.ts (the lower-level connect() / App interface used via AppProvider + useApp for @reboot-dev-style consumers) was deliberately left out of that unification to keep PR #6 scoped. It's now a parallel universe:

• Its own currentTheme: Theme (different shape — { mode, tokens }, no primaryColor).
• toolInfo and containerDimensions extracted from hostContext and stashed as separate locals on the App (app.toolInfo, app.containerDimensions).
• host-context-changed handler reconstructs theme from spec fields manually.
• No app.hostContext getter, no host-context subscription.
• React side has useConnectTheme but nothing for the broader context.

Open question (resolve first)

Is connect.ts still used by anyone? Internal NimbleBrain bundles use createSynapse, not connect(). The App / AppProvider / useApp surface was originally added for @reboot-dev-style remote MCP apps that wanted a thin imperative layer.

If no current consumer depends on it: delete it, drop the React adapters (AppProvider, useApp, useConnectTheme, useResize, useToolInput, useToolResult), and stop maintaining a parallel SDK surface. That's the highest-leverage answer.

Action: audit consumers (npm dependents + internal usage) before scoping the unification work below.

If we keep it: scope of unification

Share state shape, not implementation. Don't extract a common helper module — the two surfaces have different ergonomic shapes (typed getTheme/onThemeChanged callbacks vs. event-string app.on("theme-changed", ...)).

Estimated ~150 lines, ~5 files:

1. src/connect.ts — replace currentTheme / separate locals with currentHostContext: McpUiHostContext as single source of truth. app.theme, app.toolInfo, app.containerDimensions become getters that derive from it. host-context-changed handler replaces the whole bag (matches createSynapse semantics).
2. src/types.ts — add readonly hostContext: McpUiHostContext to the App interface. Existing fields stay (back-compat).
3. src/react/connect-hooks.ts — add useConnectHostContext<T>() mirroring useHostContext.
4. src/react/index.ts — export useConnectHostContext.
5. Tests — extend connect.test.ts for the new getter; add useConnectHostContext to __tests__/react/connect-hooks.test.tsx.

Out of scope

• Extracting a shared host-context.ts module that both createSynapse and connect import from. Forces one ergonomic shape onto two consumers.
• Unifying React hook names (useHostContext vs useConnectHostContext). The two SDK surfaces stay distinct by design.