✨ Add configurable transaction filtering system

Implement YAML-based merchant/description filtering with flexible pattern
matching (substring, prefix, suffix). Filtered transactions are excluded
from LLM analysis but included in summary for context.

Changes:
- Add FilterRule, FilterConfig, FilterResult models (src/models.go)
- Add YAML config loading with gopkg.in/yaml.v3 (src/settings.go, go.mod)
- Implement transaction filtering logic (src/main.go)
- Update LLM prompt to include filtered transaction summary (src/llm.go)
- Add config.example.yaml with sample filter rules
- Add .env.example with FILTER_CONFIG_PATH variable
- Update CLAUDE.md documentation with filtering feature details

Set FILTER_CONFIG_PATH env variable to enable optional filtering.

Remove BadgerDB cache to simplify notification flow

Eliminates cache-related complexity that was preventing reliable notifications.
Application now analyzes and notifies on every run when transactions exist.

Changes:
- Removed db.go and all BadgerDB dependencies
- Removed --disable-cache and --force flags
- Removed 2-day notification cooldown
- Removed account balance update tracking
- Updated documentation to reflect simplified architecture

This reduces the codebase by 272 lines and makes the application behavior
more predictable and easier to understand.

Revert "Fix: Include zero-balance credit cards in analysis"

This reverts commit e6705ad.

Fix: Include zero-balance credit cards in analysis

Zero-balance accounts were being filtered out before credit card filtering,
causing Tangerine World Mastercard to be excluded when paid off. This meant
when only TD remained and its balance_date hadn't changed, no notifications
were sent even though Tangerine had activity.

Now all accounts pass through to credit card filtering, ensuring paid-off
credit cards are still analyzed and their balance_date changes are detected.

🐛 Fix: Update Dockerfile to use Go 1.24

Update base image from golang:1.22-alpine to golang:1.24-alpine
to match go.mod requirement of Go 1.24.0, fixing CI build failure.

⬆️ Upgrade dependencies and add spending analysis features

- Upgrade all Go dependencies to latest versions (Go 1.24, Badger 4.8, etc.)
- Add credit card account filtering (default: analyze credit cards only)
- Add daily burn rate calculation and monthly projection to AI analysis
- Update documentation with account filtering details
- Mark tasks 7, 8, 9 as complete; add task 10 (transaction dates)

🔧 Config: Change default warning suffix to -warning (no 's')

📝 Docs: Add project documentation and backlog

- Add CLAUDE.md with project overview and guidelines
- Add backlog directory with task management

✨ Feat: Add 3-cycle billing analysis with reasoning support

- Add current_and_last_month date range type (now default)
- Implement multi-cycle analysis showing 3 billing periods
- Add system message to prime LLM as financial analyst
- Enable reasoning mode for complex multi-period analysis
- Add temperature control (0.4) for consistent responses
- Show per-cycle totals with trend comparisons
- Update default behavior to analyze 3 cycles instead of 1

🐛 Debug: Add logging for ntfy topic selection