feat: implement L1-L7 context tree for multi-layered memory management

Implements Pillar 2 (Multi-layered Context Management) with a 7-tier
hierarchical memory system from real-time market data to generational
trading wisdom.

## New Modules
- `src/context/layer.py`: ContextLayer enum and metadata config
- `src/context/store.py`: ContextStore for CRUD operations
- `src/context/aggregator.py`: Bottom-up aggregation (L7→L6→...→L1)

## Database Changes
- Added `contexts` table for hierarchical data storage
- Added `context_metadata` table for layer configuration
- Indexed by layer, timeframe, and updated_at for fast queries

## Context Layers
- L1 (Legacy): Cumulative wisdom (kept forever)
- L2 (Annual): Yearly metrics (10 years retention)
- L3 (Quarterly): Strategy pivots (3 years)
- L4 (Monthly): Portfolio rebalancing (2 years)
- L5 (Weekly): Stock selection (1 year)
- L6 (Daily): Trade logs (90 days)
- L7 (Real-time): Live market data (7 days)

## Tests
- 18 new tests in `tests/test_context.py`
- 100% coverage on context modules
- All 72 tests passing (54 existing + 18 new)

## Documentation
- Added `docs/context-tree.md` with comprehensive guide
- Updated `CLAUDE.md` architecture section
- Includes usage examples and best practices

Closes #15

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

src/context/layer.py

@@ -0,0 +1,75 @@
+"""Context layer definitions for multi-tier memory management."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from enum import Enum
+
+
+class ContextLayer(str, Enum):
+    """7-tier context hierarchy from real-time to generational."""
+
+    L1_LEGACY = "L1_LEGACY"  # Cumulative/generational wisdom
+    L2_ANNUAL = "L2_ANNUAL"  # Yearly performance
+    L3_QUARTERLY = "L3_QUARTERLY"  # Quarterly strategy adjustments
+    L4_MONTHLY = "L4_MONTHLY"  # Monthly rebalancing
+    L5_WEEKLY = "L5_WEEKLY"  # Weekly stock selection
+    L6_DAILY = "L6_DAILY"  # Daily trade logs
+    L7_REALTIME = "L7_REALTIME"  # Real-time market data
+
+
+@dataclass(frozen=True)
+class LayerMetadata:
+    """Metadata for each context layer."""
+
+    layer: ContextLayer
+    description: str
+    retention_days: int | None  # None = keep forever
+    aggregation_source: ContextLayer | None  # Parent layer for aggregation
+
+
+# Layer configuration
+LAYER_CONFIG: dict[ContextLayer, LayerMetadata] = {
+    ContextLayer.L1_LEGACY: LayerMetadata(
+        layer=ContextLayer.L1_LEGACY,
+        description="Cumulative trading history and core lessons learned across generations",
+        retention_days=None,  # Keep forever
+        aggregation_source=ContextLayer.L2_ANNUAL,
+    ),
+    ContextLayer.L2_ANNUAL: LayerMetadata(
+        layer=ContextLayer.L2_ANNUAL,
+        description="Yearly returns, Sharpe ratio, max drawdown, win rate",
+        retention_days=365 * 10,  # 10 years
+        aggregation_source=ContextLayer.L3_QUARTERLY,
+    ),
+    ContextLayer.L3_QUARTERLY: LayerMetadata(
+        layer=ContextLayer.L3_QUARTERLY,
+        description="Quarterly strategy adjustments, market phase detection, sector rotation",
+        retention_days=365 * 3,  # 3 years
+        aggregation_source=ContextLayer.L4_MONTHLY,
+    ),
+    ContextLayer.L4_MONTHLY: LayerMetadata(
+        layer=ContextLayer.L4_MONTHLY,
+        description="Monthly portfolio rebalancing, risk exposure, drawdown recovery",
+        retention_days=365 * 2,  # 2 years
+        aggregation_source=ContextLayer.L5_WEEKLY,
+    ),
+    ContextLayer.L5_WEEKLY: LayerMetadata(
+        layer=ContextLayer.L5_WEEKLY,
+        description="Weekly stock selection, sector focus, volatility regime",
+        retention_days=365,  # 1 year
+        aggregation_source=ContextLayer.L6_DAILY,
+    ),
+    ContextLayer.L6_DAILY: LayerMetadata(
+        layer=ContextLayer.L6_DAILY,
+        description="Daily trade logs, P&L, market summaries, decision accuracy",
+        retention_days=90,  # 90 days
+        aggregation_source=ContextLayer.L7_REALTIME,
+    ),
+    ContextLayer.L7_REALTIME: LayerMetadata(
+        layer=ContextLayer.L7_REALTIME,
+        description="Real-time positions, quotes, orderbook, volatility, live P&L",
+        retention_days=7,  # 7 days (real-time data is ephemeral)
+        aggregation_source=None,  # No aggregation source (leaf layer)
+    ),
+}