Comprehensive visual design improvements for TUI

This commit implements a complete visual redesign and refactoring to improve
consistency, accessibility, and maintainability of the TUI interface.

## New Visual Constants Module
- Created trace/tui/visual_constants.py with centralized constants:
  - Layout: Screen positioning and structure (header, content, footer)
  - Spacing: Padding and margins (dialogs, horizontal padding)
  - ColumnWidths: Fixed column widths for lists (tags, IOCs, content)
  - DialogSize: Standard dialog dimensions (small, medium, large)
  - Icons: Unicode symbols used throughout UI
  - Timing: Animation and feedback timing constants

## Color System Improvements
- Fixed duplicate color definitions (removed from tui_app.py)
- Use ColorPairs constants throughout instead of hardcoded numbers
- Separated tag colors from footer colors:
  - Tags now use magenta (ColorPairs.TAG) instead of yellow
  - Footers keep yellow (ColorPairs.WARNING) for consistency
  - Updated TAG_SELECTED to magenta on cyan
- All 129+ color_pair() calls now use semantic ColorPairs constants

## Accessibility Enhancements
- Added warning icons (⚠) to all IOC displays for visual + color cues
- Tag highlighting now uses distinct magenta color
- Improved color semantics reduce reliance on color alone
- Smart text truncation at word boundaries for better readability

## Layout & Spacing Standardization
- Replaced magic numbers with Layout/Spacing constants:
  - Footer positioning: height - Layout.FOOTER_OFFSET_FROM_BOTTOM
  - Content area: Layout.CONTENT_START_Y
  - Truncation: width - Spacing.HORIZONTAL_PADDING
  - Dialog margins: Spacing.DIALOG_MARGIN
- Standardized dialog sizes using DialogSize constants:
  - Input dialogs: DialogSize.MEDIUM
  - Multiline dialogs: DialogSize.LARGE
  - Confirm dialogs: DialogSize.SMALL (with dynamic width)
  - Settings dialog: DialogSize.MEDIUM

## User Experience Improvements
- Enhanced footer command organization with visual grouping:
  - Used Icons.SEPARATOR_GROUP (│) to group related commands
  - Example: "[n] Add Note │ [t] Tags [i] IOCs │ [v] View [e] Export"
- Smart content truncation (_safe_truncate):
  - Added word_break parameter (default True)
  - Breaks at word boundaries when >60% text retained
  - Maintains Unicode safety while improving readability
- Improved empty state messages:
  - New _draw_empty_state() helper for consistent visual structure
  - Centered boxes with proper spacing
  - Clear call-to-action hints
  - Applied to "No cases found" and "No cases match filter"

## Code Quality & Maintainability
- Eliminated hardcoded spacing values throughout 3,468-line file
- Used Icons constants for all Unicode symbols (─│┌└◆●○▸⚠⌗◈✓✗?)
- Fixed circular import issues with delayed global imports in TUI.__init__
- Updated comments to reflect new ColorPairs constants
- Consistent use of f-strings for footer construction

## Visual Consistency
- Replaced all "─" literals with Icons.SEPARATOR_H
- Standardized truncation widths (width - Spacing.HORIZONTAL_PADDING)
- Consistent use of ColumnWidths for tag (30) and IOC (50+2) displays
- All dialogs now use standard sizes from visual_constants

## Testing
- Verified no syntax errors in all modified files
- Confirmed successful module imports
- Tested CLI functionality (--help, --list)
- Backward compatibility maintained

This establishes a strong foundation for future UI enhancements while
significantly improving code maintainability and visual consistency.

trace/tui/rendering/colors.py

@@ -39,5 +39,5 @@ def init_colors():
         curses.init_pair(ColorPairs.TAG, curses.COLOR_MAGENTA, curses.COLOR_BLACK)
         # IOCs on selected background (red on cyan)
         curses.init_pair(ColorPairs.IOC_SELECTED, curses.COLOR_RED, curses.COLOR_CYAN)
-        # Tags on selected background (yellow on cyan)
-        curses.init_pair(ColorPairs.TAG_SELECTED, curses.COLOR_YELLOW, curses.COLOR_CYAN)
+        # Tags on selected background (magenta on cyan)
+        curses.init_pair(ColorPairs.TAG_SELECTED, curses.COLOR_MAGENTA, curses.COLOR_CYAN)

trace/tui/rendering/text_renderer.py

@@ -113,15 +113,15 @@ class TextRenderer:
                     screen.addstr(y, x_pos, text)
                     screen.attroff(curses.color_pair(ColorPairs.ERROR) | curses.A_BOLD)
             else:  # tag
-                # Tag highlighting: yellow on cyan if selected, yellow on black otherwise
+                # Tag highlighting: magenta on cyan if selected, magenta on black otherwise
                 if is_selected:
                     screen.attron(curses.color_pair(ColorPairs.TAG_SELECTED))
                     screen.addstr(y, x_pos, text)
                     screen.attroff(curses.color_pair(ColorPairs.TAG_SELECTED))
                 else:
-                    screen.attron(curses.color_pair(ColorPairs.WARNING))
+                    screen.attron(curses.color_pair(ColorPairs.TAG))
                     screen.addstr(y, x_pos, text)
-                    screen.attroff(curses.color_pair(ColorPairs.WARNING))
+                    screen.attroff(curses.color_pair(ColorPairs.TAG))
 
             x_pos += len(text)
             last_pos = end

trace/tui/visual_constants.py

@@ -0,0 +1,68 @@
+"""Visual constants for consistent TUI layout and styling"""
+
+
+class Layout:
+    """Screen layout constants"""
+    HEADER_Y = 0
+    HEADER_X = 2
+    CONTENT_START_Y = 2
+    CONTENT_INDENT = 4
+    FOOTER_OFFSET_FROM_BOTTOM = 3
+    BORDER_OFFSET_FROM_BOTTOM = 2
+
+
+class Spacing:
+    """Spacing and padding constants"""
+    SECTION_VERTICAL_GAP = 2
+    ITEM_VERTICAL_GAP = 1
+    DIALOG_MARGIN = 4
+    HORIZONTAL_PADDING = 6  # width - 6 for truncation
+    HASH_DISPLAY_PADDING = 20  # width - 20
+
+
+class ColumnWidths:
+    """Fixed column widths for list displays"""
+    TAG_COLUMN = 30
+    IOC_COLUMN = 50
+    CONTENT_PREVIEW = 50
+    NOTE_PREVIEW = 60
+
+
+class DialogSize:
+    """Standard dialog dimensions (width, height)"""
+    SMALL = (40, 8)   # Confirm dialogs
+    MEDIUM = (60, 15)  # Settings, single input
+    LARGE = (70, 20)   # Multiline, help
+
+
+class Icons:
+    """Unicode symbols used throughout UI"""
+    ACTIVE = "●"
+    INACTIVE = "○"
+    DIAMOND = "◆"
+    SQUARE = "■"
+    SMALL_SQUARE = "▪"
+    ARROW_RIGHT = "▸"
+    WARNING = "⚠"
+    HASH = "⌗"
+    FILTER = "◈"
+    VERIFIED = "✓"
+    FAILED = "✗"
+    UNSIGNED = "?"
+    SEPARATOR_H = "─"
+    SEPARATOR_V = "│"
+    SEPARATOR_GROUP = "│"  # For grouping footer commands
+    BOX_TL = "┌"
+    BOX_BL = "└"
+    # Box drawing for improved empty states
+    BOX_DOUBLE_TL = "╔"
+    BOX_DOUBLE_TR = "╗"
+    BOX_DOUBLE_BL = "╚"
+    BOX_DOUBLE_BR = "╝"
+    BOX_DOUBLE_H = "═"
+    BOX_DOUBLE_V = "║"
+
+
+class Timing:
+    """Timing constants"""
+    FLASH_MESSAGE_DURATION = 3  # seconds