refactor(keyretriever): reduce duplicate master-key WARN logs

[moonD4rk]

Summary

• Demote in-chain retriever failures from WARN to Debug
• GcoredumpRetriever falls through silently on internal failures
• Dedupe master-key WARN per browser instead of per profile
• Clarify "exit status 128 ()" with empty stderr message

Test plan

• golangci-lint run clean
• go test ./... passes
• Manual smoke on macOS multi-profile: 46 WARN → 3 WARN

Closes #588

[codecov-commenter]

Codecov Report

❌ Patch coverage is 16.66667% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.60%. Comparing base (50c4ea8) to head (9386ca6).

Files with missing lines	Patch %	Lines
browser/chromium/chromium.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #589      +/-   ##
==========================================
+ Coverage   71.25%   73.60%   +2.35%     
==========================================
  Files          61       61              
  Lines        3294     2815     -479     
==========================================
- Hits         2347     2072     -275     
+ Misses        757      553     -204     
  Partials      190      190              

Flag	Coverage Δ
unittests	73.60% <16.66%> (+2.35%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Pull request overview

This PR refactors Chromium master-key retrieval logging to reduce repeated WARN-level messages during multi-profile extraction, particularly on macOS when key retrieval commonly fails in expected ways (e.g., no keychain access / not root).

Changes:

• Demotes per-retriever failures inside ChainRetriever from WARN to Debug to avoid noisy “expected failure” logs.
• Updates macOS GcoredumpRetriever to silently fall through (return (nil, nil)) on internal failures while logging only at Debug.
• Deduplicates “master key retrieval” WARN logs across Chromium profiles by emitting a WARN once and subsequent failures as Debug; also improves security command error clarity when stderr is empty.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
crypto/keyretriever/keyretriever_darwin.go	Adjusts macOS retrievers to avoid repeated warning-worthy failures; improves security error messaging.
crypto/keyretriever/keyretriever.go	Demotes in-chain retriever failure logs from WARN to Debug.
browser/chromium/chromium.go	Adds per-browser WARN deduplication for master-key retrieval failures.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.