feat: detect Apex logs in .log/.txt files with content-based analysis

[lukecotter]

📝 PR Overview

Adds content-based Apex log detection so that .log and .txt files containing Apex debug logs get full extension support (decorations, CodeLens, context menus) without requiring manual language association.

🛠️ Changes made

• Add ApexLogLanguageDetector that auto-detects Apex log content in .log/.txt files and sets the apexlog language
• Set lana.isApexLog context key for detected files, enabling menus/commands on large files (>50MB) where activeTextEditor is unavailable
• Update ShowAnalysisCodeLens to register on .log/.txt files with runtime isApexLogContent guard
• Update LogTimingDecoration and RawLogLineDecoration to use content-based detection instead of languageId check
• Remove .log/.txt from static language extensions in package.json (detection is now dynamic)
• Add onStartupFinished activation event for early detection
• Simplify isApexLogFile to use sync openSync/readSync/closeSync for 4KB reads instead of async streams
• Use extname() from node:path instead of manual string slicing

🧩 Type of change (check all applicable)

• 🐛 Bug fix - something not working as expected
• ✨ New feature – adds new functionality
• ♻️ Refactor - internal changes with no user impact
• ⚡ Performance Improvement
• 📝 Documentation - README or documentation site changes
• 🔧 Chore - dev tooling, CI, config
• 💥 Breaking change

🔗 Related Issues

✅ Tests added?

• 👍 yes
• 🙅 no, not needed

📚 Docs updated?

• 🙅 not needed

Anything else we need to know?

• isApexLogFile (sync disk read) is only used for the tab-API fallback path when files are >50MB and activeTextEditor is undefined. The 4KB sync read completes in <1ms.
• The pre-existing SalesforceConnection.ts type error is unrelated to this PR.