feat: implement chart container with state-based rendering (Task 2.4)

- Add chart_loading_skeleton() with animated bar chart and spinner
- Add chart_error_state() for displaying errors with guidance
- Add chart_empty_state() for when filters yield no results
- Add chart_ready_placeholder() for Phase 4 Plotly integration
- Rewrite chart_section() with 4-state rx.cond() logic
- Fix icon names (triangle-alert) and color references (SLATE_500)

This completes Phase 2 Layout Components.

progress.txt

@@ -323,3 +323,70 @@ Use `rx.cond(condition, true_value, false_value)` not Python `if`.
 ### Blocked items:
 - Debounced filter handlers (300ms) deferred to Phase 3.3
 - Visual validation still blocked until rxconfig is updated
+
+## Iteration 6 - 2026-02-04
+### Task: 2.4 Chart Container
+### Why this task:
+- Previous iteration (5) explicitly recommended continuing with Task 2.4
+- Natural completion of Phase 2 Layout Components
+- Chart container is foundational for Phase 4 Plotly integration
+- No dependencies blocking this task
+### Status: COMPLETE
+### What was done:
+- Created `chart_loading_skeleton()` component:
+  - Animated bar chart skeleton with 6 bars at different heights
+  - Uses CSS pulse animation (1.5s infinite) with staggered delays
+  - Spinner + "Generating chart..." text below
+  - Design tokens used (Colors, Typography, Spacing, Radii)
+- Created `chart_error_state(error_message)` component:
+  - Triangle alert icon (48px, warning color)
+  - "Unable to Generate Chart" heading
+  - Dynamic error message from state
+  - Helpful guidance text for resolution
+- Created `chart_empty_state()` component:
+  - Search-x icon (48px, slate color)
+  - "No Data to Display" heading
+  - Message explaining no records match filters
+  - Guidance to widen filters
+- Created `chart_ready_placeholder()` component:
+  - Chart-bar-stacked icon (primary blue)
+  - "Chart Ready" heading
+  - Pale blue background with dashed primary border
+  - Clear indication that Plotly renders here in Phase 4
+- Rewrote `chart_section()` with state-based rendering:
+  - Header row: title + chart hierarchy info
+  - Uses nested rx.cond() for 4-state logic:
+    1. Loading (chart_loading=True) → skeleton
+    2. Error (error_message!="") → error state
+    3. Empty (data_loaded & unique_patients==0) → empty state
+    4. Ready → placeholder
+  - Full-width card styling
+- Fixed icon names: alert-triangle → triangle-alert (Lucide convention)
+- Fixed Colors.SLATE_400 → SLATE_500 (SLATE_400 doesn't exist in palette)
+### Validation results:
+- Tier 1 (Code):
+  - `python -m py_compile pathways_app/app_v2.py` PASSED
+  - `python -c "from pathways_app.app_v2 import app"` PASSED
+  - All 5 chart component functions return Box type correctly
+- Tier 2 (Visual): Deferred - requires modifying rxconfig to test app_v2
+- Tier 3 (Functional): State-based rendering verified structurally via rx.cond nesting
+### Files changed:
+- Modified: pathways_app/app_v2.py (+180 lines - 4 new components, rewritten chart_section)
+- Modified: IMPLEMENTATION_PLAN.md (marked 2.4 subtasks complete)
+### Committed: [pending]
+### Patterns discovered:
+- Lucide icon names: triangle-alert not alert-triangle, search-x works
+- CSS animations in Reflex: use animation prop with standard CSS syntax
+- Staggered animations: animation_delay="0.1s" works for sequential delays
+- Nested rx.cond() for multi-state logic: readable priority chain
+- Colors.SLATE_400 doesn't exist in design system - use 300/500 instead
+### Next iteration should:
+- Phase 2 is now COMPLETE. Start Phase 3: State Management
+- Task 3.1: Core State Variables - many already exist from Task 2.2, needs review
+- Task 3.2: Data Loading - create load_data() to read from SQLite
+  - Reference data_processing/loader.py for SQLite patterns
+  - Populate available_drugs, available_indications, available_directorates from data
+  - Detect latest date for "to" date defaults
+- Consider testing app_v2 visually by modifying pathways_app/__init__.py to import from app_v2
+### Blocked items:
+- Visual validation still blocked until rxconfig is updated to point to app_v2