Add export CLI command for CSV/JSON data export

[nandanadileep]

Summary

Fixes #13 by adding a direct database export path for users who want to analyze trends externally, share cost data, or back up before clear.

• context-analyzer-tool export with --format csv|json, required --table, optional --output, and optional --days
• Supports events, tasks, snapshots (maps to token_snapshots), and anomalies
• Opens the local SQLite DB directly (same pattern as prune)
• New db/export.py module for row fetching and serialization
• Tests cover day filtering, table aliases, CSV/JSON formatting, and CLI file/stdout output

Usage

context-analyzer-tool export --format csv --table tasks --output tasks.csv
context-analyzer-tool export --format json --table anomalies
context-analyzer-tool export --format csv --table snapshots --days 7

Test plan

• uv run pytest tests/test_export.py -q (7 passed)
• uv run ruff check on changed files
• Export each table to CSV and open in a spreadsheet
• Verify --days 7 only includes recent rows

Made with Cursor