[feature] Subscription Service Price Tracker with Interactive Stock-Style Charts and Proactive Alerts

**Title:** Feature Proposal: Subscription Service Price Tracker with Interactive Stock-Style Charts and Proactive Alerts

**Is your feature request related to a problem? Please describe.**

Many individuals monitor recurring subscription costs—particularly for streaming and media services such as Netflix, Hulu, YouTube TV, Spotify, and similar platforms—to track long-term price inflation, anticipate increases, and evaluate ongoing value. While changedetection.io provides excellent general website change detection and single-product price monitoring, it lacks specialized support for subscription ecosystems, including:

- Curated presets for popular subscription services and their tiered plans
- Rich, interactive historical trend visualization comparable to stock price trackers or PCPartPicker component histories
- Multi-service and multi-tier comparison within a single view
- Contextual annotations from official vendor announcements
- Advanced alerting tied to personal budget thresholds and cancellation guidance

Current price detection is well-suited to e-commerce but does not fully address the characteristics of subscription pricing: infrequent yet significant discrete increases, multiple plan tiers per service, regional variations, and the value of long-horizon (5–10+ year) historical context.

**Describe the solution you'd like**

Introduce a "Subscription Price Tracker" module or dedicated mode that extends the existing price detection and notification capabilities with subscription-specific features. The proposed components are:

1. **Pre-configured Subscription Presets**
Deliver a curated library of URLs and selectors for major subscription services (e.g., Netflix, Hulu, YouTube TV, Spotify, Disney+, Amazon Prime Video, Apple TV+, Paramount+, others).
- Support multiple plan tiers per service (Basic, Standard, Premium, Family, etc.)
- Enable straightforward user extension for additional services or regional pricing pages

2. **Historical Data Seeding & Import**
Allow one-time import of verified historical pricing data spanning 5–10+ years from authoritative sources, including:
- CableTV.com streaming price tables
- FinanceBuzz.com historical summaries
- Cross-verified Wikipedia timelines
- Official company newsroom and investor-relations archives
This would seed the history database immediately, enabling meaningful trend analysis from initial setup while ongoing watchers capture future changes.

3. **Interactive Stock-Style Visualization for Price Trends**
Add a dedicated visualization panel or dashboard tab featuring flexible, interactive charts modeled after stock price trackers:
- **Supported chart types**: Line (clean trend overview), Area/Mountain (shaded to highlight cumulative change), Candle (adapted for discrete price steps, showing magnitude of increases), OHLC bar (where useful for emphasizing adjustment points)
- **Core interactivity**: Zoom, pan, crosshair tooltips with exact date, price, and percentage change; toggle between monthly, quarterly, and yearly aggregation
- **Multi-series comparison**: Overlay multiple services and plan tiers in the same chart window (e.g., Netflix Premium, Hulu With Ads, Spotify Family) for direct side-by-side analysis of inflation trajectories
- **Visual controls**: Color-coded legends, series visibility toggles, synchronized axes across overlaid datasets
- **Annotations**: Place vertical markers or callouts at significant price changes, linking to (or summarizing) corresponding vendor blog posts or press releases (e.g., “Netflix Jan 2025 increase: +$2–3 for content investment”)

4. **Enhanced Alerting & Budget Management Tools**
Extend the notification framework with subscription-oriented triggers:
- Email, webhook, or integration alerts when a price increase exceeds a user-defined percentage or absolute threshold
- “Budget cap” notifications suggesting cancellation or review when a plan surpasses a personal maximum (e.g., “Netflix Premium > $25 → consider lower-cost alternatives”)
- Future extension: Neutral, community-sourced recommendations for comparable lower-priced services

**Describe alternatives you've considered**

- Static articles and tables (CableTV.com, FinanceBuzz, PCMag) offer historical data but provide no real-time monitoring, interactive filtering, multi-service comparison, or proactive alerts
- Personal subscription managers (Wallos, SubTrackr) track individual expenses but do not scrape public pricing pages or generate cross-vendor trend visualizations
- General change-detection tools focus on products rather than subscription models with tiered plans and infrequent updates

**Additional context**

This feature would meaningfully expand changedetection.io’s utility for consumers facing subscription cost creep, while remaining fully self-hosted and privacy-respecting. It leverages existing strengths (price extraction, history storage, Playwright support, notifications) and can be delivered incrementally:

- Phase 1: Preset library + historical data import
- Phase 2: Multi-type charting engine with multi-series overlay support
- Phase 3: Advanced alerts, budget caps, and vendor announcement annotations

I am prepared to contribute selectors, import scripts, or visualization prototypes. If useful, I can supply initial wireframes or example selectors for priority services.

Thank you for considering this proposal. It would provide a powerful, community-oriented tool for subscription price transparency and cost-awareness.