feat: Add tabs Layout

[DhruvLohar]

Summary

This PR adds two quality-of-life features to the database UI: a persistent tabbed interface for working across multiple tables simultaneously, and a one-click copy button on every table
cell.

---

Tabbed Table Navigation

Opens each table in a tab at the top of the content area, similar to how a database client like TablePlus or DBeaver works.

Behaviour:

• Clicking any table in the sidebar opens it as a new tab
• Tabs persist across hard refreshes via localStorage — reloading the page restores your full session
• Filters, sorts, and pagination are saved per-tab — switching away and back restores the exact state you left
• Closing the active tab navigates to the left neighbour (falls back right if it's the first tab)
• Clicking the already-active tab is a no-op (no unnecessary re-navigation)
• Tab bar scrolls horizontally when overflow occurs; active tab is always scrolled into view when navigating from the sidebar
• Tab labels show the table name only (strips schema prefix for brevity); full schema.table stored internally

Files added/changed:

• src/lib/TabsContext.tsx — React context with localStorage hydration, openTab / updateTabHref / closeTab
• src/components/TableTabs.tsx — tab bar UI component
• src/app/layout.tsx — wraps app in TabsProvider, renders TableTabs above main content
• src/app/[tableName]/TablePageClient.tsx — registers tab on mount, syncs href on every filter/sort/page change

---

Click-to-Copy on Table Cells

Every cell in every table now has a copy button that appears on row hover.

Behaviour:

• Hover a row to reveal the copy icon on each cell
• Click copies the cell value to clipboard
• Icon flips to a green checkmark and a "Copied!" tooltip appears for 1.5s, then resets
• Uses the existing @radix-ui/react-tooltip — no new dependencies added
• CopyableCell is wrapped in React.memo to avoid unnecessary re-renders across large tables

Files added/changed:

• src/components/CopyableCell.tsx — copy button with tooltip feedback
• src/components/TableDisplay.tsx — renders CopyableCell for every cell, added "use client" directive

---

Screenshots

---