Add Native Summary Row / Footer to Table Component with Search-Aware Aggregations

**Summary**
The Table component currently lacks **any** ability to display column totals or summaries at the bottom. Users are requesting a native **Footer Row** feature to display aggregations (Sum, Count, Average) for numeric and text columns.
**Crucial requirement:** These totals must dynamically recalculate based on the user's **Search Query** and **In-App Filters**. A static total of the entire database is not useful; users need to see the total for the *currently visible* rows.

**Current Problem**
* **Missing Core Feature:** Unlike standard spreadsheets (Excel, Google Sheets) or competing no-code grids, Glide Tables currently cannot show a simple "Total" at the bottom of a Price column. The table is just an endless list of rows with no summary context.
* **No "View-Based" Math:** Developers can calculate total sums in the backend (Data Editor), but these are static. There is no way to calculate the sum of *only* the items the user has filtered on the screen (e.g., "Show me total value of invoices found by search 'Service'").
* **Disconnected UI:** To show a total, developers currently have to place a separate "Big Number" component *above* the table. This is confusing because if the user filters the table, the Big Number above stays the same (it doesn't react to the table's search bar).

**Examples/Scenarios**
* **Invoicing:** A user sees a list of 50 invoices. They search for "Acme Corp". The table filters to show 3 rows. The user expects to see the **Total Sum** of just those 3 invoices at the bottom of the "Amount" column.
* **Inventory:** A user filters by "Category: Electronics". The footer should show "Count: 15 items" and "Total Value: $5,000".

**Suggested UX**
* **New Setting:** Add a "Show Footer / Summary Row" toggle in the Table configuration.
* **Column Options:** Allow selecting an aggregation type for each column (Sum, Average, Min, Max, Count, Empty).
* **Behavior:**
1. Display a sticky row at the bottom of the table.
2. **Update in Real-Time:** As the user types in the Search Bar or changes a Filter, the footer numbers must instantly update to reflect only the data currently shown.