feat: centralize state management with React Context

[shivv23]

Introduces React Context to centralize shared state management, eliminating prop drilling across the Home route component tree.

Motivation

All shared state (selectedFile, billType, showMenu) was owned by Home.tsx and passed as props to Dashboard, NewFile, and Menu. Additionally, a Local store instance was created inside the component body on every render — a performance anti-pattern that allocates a new object each cycle.

Changes

New context providers (src/contexts/):

• StoreContext.tsx — provides a singleton Local instance via useMemo, wrapped in a useStore() hook. Mounted at the App level so both Home and MeshKitPage share the same instance.
• InvoiceContext.tsx — provides selectedFile, billType, showMenu and their setters via a useInvoice() hook. Mounted at the Home level where the state is owned.

Refactored components:

Component	Before	After
Home.tsx	Owned state, passed 4-6 props to each child	Provides InvoiceContext, renders children with zero props
Dashboard.tsx	Received store, currentBillType, onOpenFile as props	Consumes useStore() and useInvoice(), receives only onOpenFile
NewFile.tsx	Received file, store, billType, updateSelectedFile as props	Consumes useStore() and useInvoice(), zero props
Menu.tsx	Received showM, setM, file, updateSelectedFile, store, bT as props	Consumes useStore() and useInvoice(), zero props
MeshKitPage.tsx	Created new Local() on every render	Consumes useStore() for singleton instance

App.tsx — wraps the router in <StoreProvider> to make the singleton store available app-wide.

Dead code removal:

• Deleted src/components/Files/ (346 lines) — never imported by any component, legacy artifact superseded by Dashboard.

Type infrastructure:

• Added src/types/meshkit-ionic.d.ts type declaration stub for @meshkit/ionic (local file dependency without published types).

Architecture

<App>
  <StoreProvider>              // singleton Local instance
    <Home>
      <InvoiceContext.Provider>  // selectedFile, billType, showMenu
        <Dashboard />           // useStore() + useInvoice()
        <NewFile />             // useStore() + useInvoice()
        <Menu />                // useStore() + useInvoice()
      </InvoiceContext.Provider>
    </Home>
    <MeshKitPage />             // useStore() only
  </StoreProvider>
</App>

Benefits

• No more prop drilling — consumers access shared state directly via hooks
• Consistent naming — selectedFile and billType everywhere (no more file/bT/currentBillType variants)
• Singleton store — useMemo ensures one Local instance across all renders
• Type-safe context — custom hooks throw if used outside their provider, catching misconfiguration at runtime
• ~376 lines of dead code removed (Files component)

Verification

npx tsc --noEmit passes with zero errors (excluding the pre-existing @meshkit/ionic module resolution addressed by PR #1).