feat: implement daily trading mode with batch decisions (issue #57)

Add API-efficient daily trading mode for Gemini Free tier compatibility:

## Features

- **Batch Decisions**: GeminiClient.decide_batch() analyzes multiple stocks
  in a single API call using compressed JSON format
- **Daily Trading Mode**: run_daily_session() executes N sessions per day
  at configurable intervals (default: 4 sessions, 6 hours apart)
- **Mode Selection**: TRADE_MODE env var switches between daily (batch)
  and realtime (per-stock) modes
- **Requirements Log**: docs/requirements-log.md tracks user feedback
  chronologically for project evolution

## Configuration

- TRADE_MODE: "daily" (default) | "realtime"
- DAILY_SESSIONS: 1-10 (default: 4)
- SESSION_INTERVAL_HOURS: 1-24 (default: 6)

## API Efficiency

- 2 markets × 4 sessions = 8 API calls/day (within Free tier 20 calls)
- 3 markets × 4 sessions = 12 API calls/day (within Free tier 20 calls)

## Testing

- 9 new batch decision tests (all passing)
- All existing tests maintained (298 passed)

## Documentation

- docs/architecture.md: Trading Modes section with daily vs realtime
- CLAUDE.md: Requirements Management section
- docs/requirements-log.md: Initial entries for API efficiency needs

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

CLAUDE.md

@@ -53,6 +53,7 @@ Get real-time alerts for trades, circuit breakers, and system events via Telegra
 - **[Context Tree](docs/context-tree.md)** — L1-L7 hierarchical memory system
 - **[Testing](docs/testing.md)** — Test structure, coverage requirements, writing tests
 - **[Agent Policies](docs/agents.md)** — Prime directives, constraints, prohibited actions
+- **[Requirements Log](docs/requirements-log.md)** — User requirements and feedback tracking
 
 ## Core Principles
 
@@ -61,6 +62,15 @@ Get real-time alerts for trades, circuit breakers, and system events via Telegra
 3. **Issue-Driven Development** — All work goes through Gitea issues → feature branches → PRs
 4. **Agent Specialization** — Use dedicated agents for design, coding, testing, docs, review
 
+## Requirements Management
+
+User requirements and feedback are tracked in [docs/requirements-log.md](docs/requirements-log.md):
+
+- New requirements are added chronologically with dates
+- Code changes should reference related requirements
+- Helps maintain project evolution aligned with user needs
+- Preserves context across conversations and development cycles
+
 ## Project Structure
 
 ```