Add Clide project structure and initial implementation

Set up the TUI IDE wrapper for Claude Code CLI with:
- Core app structure using Textual framework
- Panel architecture (sidebar, workspace, claude, context)
- Theme system with 22 built-in themes (Summer Night default)
- Pydantic models for configuration and data
- Makefile for development commands
- Project documentation and specs

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/snapshots/__init__.py

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+"""Snapshot (visual regression) tests for Clide."""

tests/snapshots/test_app_snapshots.py

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+"""Snapshot tests for Clide UI."""
+
+from clide.app import ClideApp
+
+
+def test_initial_layout(snap_compare) -> None:
+    """Test the initial application layout renders correctly."""
+    app = ClideApp(test_mode=True)
+    assert snap_compare(app, terminal_size=(120, 40))
+
+
+def test_layout_without_right_panel(snap_compare) -> None:
+    """Test layout with right panel hidden."""
+
+    async def hide_right_panel(pilot):
+        await pilot.press("f2")
+
+    app = ClideApp(test_mode=True)
+    assert snap_compare(
+        app,
+        terminal_size=(120, 40),
+        run_before=hide_right_panel,
+    )
+
+
+def test_layout_without_left_panel(snap_compare) -> None:
+    """Test layout with left panel hidden."""
+
+    async def hide_left_panel(pilot):
+        await pilot.press("f1")
+
+    app = ClideApp(test_mode=True)
+    assert snap_compare(
+        app,
+        terminal_size=(120, 40),
+        run_before=hide_left_panel,
+    )