🛡️ Sentinel: [HIGH] Fix sensitive data leak in telemetry logs

[jhweb]

🚨 Severity: HIGH
💡 Vulnerability: Sensitive data (API keys, absolute home directory paths) was being leaked into the markdown debug reports (.logs/braindrain_debug_report_*.md) when passed in the context argument of log_error.
🎯 Impact: Exposure of user credentials and system paths in plain-text log files.
🔧 Fix: Implemented a recursive _sanitize_data helper in TelemetrySession that redacts sensitive patterns from strings, dictionaries, and lists. Updated log_error to use this helper for all logged data.
✅ Verification: Verified using a reproduction script that confirmed both absolute paths and API keys are now redacted in the debug reports. Ran existing test suite to ensure no regressions.

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PR created automatically by Jules for task 15599549885254155288 started by @jhweb

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