Add date picker for search date/before/after keywords

- Add DatePickerModal using MonthCalendar widget from calendar app
- Detect when user types 'date ', 'before ', or 'after ' and show picker
- Insert selected date (YYYY-MM-DD format) into search input
- Support keyboard navigation (left/right for months, Enter to select)
- Today button for quick selection of current date

src/mail/screens/SearchPanel.py

@@ -4,8 +4,10 @@ Provides a search input docked to the top of the window with:
 - Live search with 1 second debounce
 - Cancel button to restore previous state
 - Help button showing Himalaya search syntax
+- Date picker for date/before/after keywords
 """
 
+from datetime import date
 from typing import Optional, List, Dict, Any
 
 from textual.app import ComposeResult
@@ -19,6 +21,8 @@ from textual.widget import Widget
 from textual.widgets import Button, Input, Label, Static
 from textual.suggester import SuggestFromList
 
+from src.calendar.widgets.MonthCalendar import MonthCalendar
+
 # Himalaya search keywords for autocomplete
 HIMALAYA_KEYWORDS = [
     "from ",
@@ -132,6 +136,94 @@ class SearchHelpModal(ModalScreen[None]):
         self.dismiss(None)
 
 
+class DatePickerModal(ModalScreen[Optional[date]]):
+    """Modal with a calendar for selecting a date."""
+
+    DEFAULT_CSS = """
+    DatePickerModal {
+        align: center middle;
+    }
+
+    DatePickerModal > Vertical {
+        width: 30;
+        height: auto;
+        border: solid $primary;
+        background: $surface;
+        padding: 1 2;
+    }
+
+    DatePickerModal > Vertical > Label {
+        width: 100%;
+        text-align: center;
+        margin-bottom: 1;
+    }
+
+    DatePickerModal > Vertical > Horizontal {
+        height: auto;
+        align: center middle;
+        margin-top: 1;
+    }
+
+    DatePickerModal > Vertical > Horizontal > Button {
+        margin: 0 1;
+    }
+    """
+
+    BINDINGS = [
+        Binding("escape", "cancel", "Cancel"),
+        Binding("left", "prev_month", "Previous month", show=False),
+        Binding("right", "next_month", "Next month", show=False),
+        Binding("enter", "select_date", "Select date", show=False),
+    ]
+
+    def __init__(self, keyword: str = "date") -> None:
+        super().__init__()
+        self.keyword = keyword
+
+    def compose(self) -> ComposeResult:
+        with Vertical():
+            yield Label(f"Select date for '{self.keyword}':", id="picker-title")
+            yield MonthCalendar(id="date-picker-calendar")
+            with Horizontal():
+                yield Button("Today", variant="default", id="today-btn")
+                yield Button("Select", variant="primary", id="select-btn")
+                yield Button("Cancel", variant="warning", id="cancel-btn")
+
+    def on_month_calendar_date_selected(
+        self, event: MonthCalendar.DateSelected
+    ) -> None:
+        """Handle date selection from calendar click."""
+        self.dismiss(event.date)
+
+    def on_button_pressed(self, event: Button.Pressed) -> None:
+        if event.button.id == "select-btn":
+            calendar = self.query_one("#date-picker-calendar", MonthCalendar)
+            self.dismiss(calendar.selected_date)
+        elif event.button.id == "today-btn":
+            calendar = self.query_one("#date-picker-calendar", MonthCalendar)
+            today = date.today()
+            calendar.selected_date = today
+            calendar.display_month = today.replace(day=1)
+            calendar.refresh()
+        elif event.button.id == "cancel-btn":
+            self.dismiss(None)
+
+    def action_cancel(self) -> None:
+        self.dismiss(None)
+
+    def action_prev_month(self) -> None:
+        calendar = self.query_one("#date-picker-calendar", MonthCalendar)
+        calendar.prev_month()
+
+    def action_next_month(self) -> None:
+        calendar = self.query_one("#date-picker-calendar", MonthCalendar)
+        calendar.next_month()
+
+    def action_select_date(self) -> None:
+        calendar = self.query_one("#date-picker-calendar", MonthCalendar)
+        self.dismiss(calendar.selected_date)
+
+
 class SearchPanel(Widget):
     """Docked search panel with live search capability."""
 
@@ -216,6 +308,7 @@ class SearchPanel(Widget):
         super().__init__(name=name, id=id, classes=classes)
         self._debounce_timer: Optional[Timer] = None
         self._last_query: str = ""
+        self._pending_date_keyword: Optional[str] = None  # Track keyword awaiting date
 
     def compose(self) -> ComposeResult:
         with Horizontal():
@@ -304,6 +397,34 @@ class SearchPanel(Widget):
             self.is_searching = True
             self.post_message(self.SearchRequested(query))
 
+    def _check_date_keyword(self, value: str) -> Optional[str]:
+        """Check if the input ends with a date keyword that needs a date picker.
+
+        Returns the keyword (date/before/after) if found, None otherwise.
+        """
+        value_lower = value.lower()
+        for keyword in ("date ", "before ", "after "):
+            if value_lower.endswith(keyword):
+                return keyword.strip()
+        return None
+
+    def _show_date_picker(self, keyword: str) -> None:
+        """Show the date picker modal for the given keyword."""
+        self._pending_date_keyword = keyword
+
+        def on_date_selected(selected_date: Optional[date]) -> None:
+            if selected_date:
+                # Insert the date into the search input
+                input_widget = self.query_one("#search-input", Input)
+                date_str = selected_date.strftime("%Y-%m-%d")
+                input_widget.value = input_widget.value + date_str
+                input_widget.cursor_position = len(input_widget.value)
+            self._pending_date_keyword = None
+            # Refocus the input
+            self.query_one("#search-input", Input).focus()
+
+        self.app.push_screen(DatePickerModal(keyword), on_date_selected)
+
     def on_input_changed(self, event: Input.Changed) -> None:
         """Handle input changes with debounce."""
         if event.input.id != "search-input":
@@ -316,6 +437,12 @@ class SearchPanel(Widget):
         if not event.value.strip():
             return
 
+        # Check for date keywords and show picker
+        date_keyword = self._check_date_keyword(event.value)
+        if date_keyword:
+            self._show_date_picker(date_keyword)
+            return
+
         # Set up new debounce timer (1 second)
         self._debounce_timer = self.set_timer(1.0, self._trigger_search)