Add command_palette command to display bound keys

Add a Go-based command_palette kitten that provides a searchable,
interactive overlay for browsing and triggering keyboard shortcuts
and actions.

- New Go kitten at kittens/command_palette/ with FZF fuzzy search,
  grouped/flat views, and remote control action triggering
- Python collect_keys_data() does data collection, passed via stdin
- Navigation: arrows, ctrl+j/k (vim), ctrl+n/p (emacs), page up/down
- Enter triggers the selected action via RC command
- Help text displayed in footer for selected binding
- Added Go tests (main_test.go) and Python tests (command_palette.py)

kitty_tests/command_palette.py

@@ -0,0 +1,99 @@
+#!/usr/bin/env python
+# License: GPLv3 Copyright: 2024, Kovid Goyal <kovid at kovidgoyal.net>
+
+from . import BaseTest
+
+
+class TestCommandPalette(BaseTest):
+
+    def test_collect_keys_data(self):
+        from kittens.command_palette.main import collect_keys_data
+        from kitty.actions import groups
+        opts = self.set_options()
+        data = collect_keys_data(opts)
+        self.assertIn('modes', data)
+        self.assertIn('mouse', data)
+        self.assertIn('', data['modes'], 'Default keyboard mode should be present')
+        default_mode = data['modes']['']
+        # Should have at least some categories
+        self.assertTrue(len(default_mode) > 0, 'Should have at least one category')
+        # All category names should be from the known groups
+        known_titles = set(groups.values())
+        for cat_name in default_mode:
+            self.assertIn(cat_name, known_titles, f'Unknown category: {cat_name}')
+        # Each category should have bindings with required fields
+        for cat_name, bindings in default_mode.items():
+            self.assertIsInstance(bindings, list)
+            for b in bindings:
+                self.assertIn('key', b)
+                self.assertIn('action', b)
+                self.assertIn('action_display', b)
+                self.assertIn('help', b)
+                self.assertIn('long_help', b)
+                self.assertIsInstance(b['key'], str)
+                self.assertIsInstance(b['action'], str)
+                self.assertTrue(len(b['key']) > 0)
+                self.assertTrue(len(b['action']) > 0)
+        # Mouse mappings
+        self.assertIsInstance(data['mouse'], list)
+        for b in data['mouse']:
+            self.assertIn('key', b)
+            self.assertIn('action', b)
+            self.assertIn('action_display', b)
+
+    def test_collect_keys_categories_ordered(self):
+        from kittens.command_palette.main import collect_keys_data
+        from kitty.actions import groups
+        opts = self.set_options()
+        data = collect_keys_data(opts)
+        default_mode = data['modes']['']
+        cat_names = list(default_mode.keys())
+        group_titles = list(groups.values())
+        # Categories should appear in the same order as defined in groups
+        indices = []
+        for cat in cat_names:
+            if cat in group_titles:
+                indices.append(group_titles.index(cat))
+        self.ae(indices, sorted(indices), 'Categories should be ordered according to groups dict')
+
+    def test_collect_keys_bindings_sorted(self):
+        from kittens.command_palette.main import collect_keys_data
+        opts = self.set_options()
+        data = collect_keys_data(opts)
+        for cat_name, bindings in data['modes'][''].items():
+            keys = [b['key'] for b in bindings]
+            self.ae(keys, sorted(keys), f'Bindings in {cat_name} should be sorted by key')
+
+    def test_collect_keys_has_help_text(self):
+        from kittens.command_palette.main import collect_keys_data
+        opts = self.set_options()
+        data = collect_keys_data(opts)
+        # At least some bindings should have help text
+        has_help = False
+        for cat_name, bindings in data['modes'][''].items():
+            for b in bindings:
+                if b['help']:
+                    has_help = True
+                    break
+            if has_help:
+                break
+        self.assertTrue(has_help, 'At least some bindings should have help text')
+
+    def test_ordering_arrays_present(self):
+        from kittens.command_palette.main import collect_keys_data
+        opts = self.set_options()
+        data = collect_keys_data(opts)
+        # mode_order should list all modes
+        self.assertIn('mode_order', data)
+        self.assertIsInstance(data['mode_order'], list)
+        self.ae(set(data['mode_order']), set(data['modes'].keys()))
+        # category_order should list categories for each mode
+        self.assertIn('category_order', data)
+        self.assertIsInstance(data['category_order'], dict)
+        for mode_name in data['modes']:
+            self.assertIn(mode_name, data['category_order'])
+            self.ae(
+                set(data['category_order'][mode_name]),
+                set(data['modes'][mode_name].keys()),
+                f'category_order for mode {mode_name!r} should match modes keys',
+            )