Validate and normalize tracker player input (Steam/BattleMetrics IDs + URLs)

[FaiThiX]

Summary

This PR validates and normalizes tracker player input before saving it, so malformed values can no longer break tracker management.

Closes #14

Problem

Tracker player entries previously accepted arbitrary raw input.
That allowed invalid values to be stored, which could lead to:

• broken tracker entries,
• failed removals,
• and in some cases tracker cleanup issues.

What changed

• Added a dedicated tracker input parser used by both Add Player and Remove Player flows.
• Supported/normalized input formats:
• SteamID64 (7656119...)
• BattleMetrics player ID (12345678)
• Steam profile URL (https://steamcommunity.com/profiles/<steamid64>)
• Steam vanity URL (https://steamcommunity.com/id/<name>) -> resolved to SteamID64
• BattleMetrics player URL (https://www.battlemetrics.com/players/<id>)
• Invalid or unsupported input now returns a clear user-facing error instead of being saved.
• Remove flow now uses the same parsing logic and includes a fallback to remove legacy malformed raw entries.

Implementation details

• Added: src/util/trackerInputParser.js
• Updated: src/handlers/modalHandler.js
• Updated: src/util/scrape.js (vanity -> SteamID64 resolver)
• Updated: src/languages/en.json (new validation error message)

Validation

• node --check src/handlers/modalHandler.js
• node --check src/util/trackerInputParser.js
• node --check src/util/scrape.js
• npm test -- --pretty false

Impact

• Tracker data is now stored in consistent internal formats.
• Invalid tracker input is rejected early with clear feedback.
• Improves tracker stability without changing existing tracker behavior for valid inputs.