feat(tracing): add breadcrumbs/event trail system

[Naoray]

Summary

• Adds a BreadcrumbCollector that captures an ordered trail of log messages and cache events leading up to an error, providing pre-error context similar to Sentry/Flare breadcrumbs
• Implements a ring buffer (configurable limit, default 40) that stores timestamped entries with category, message, and optional metadata
• Formats breadcrumbs as a readable markdown table in GitHub issues/comments via BreadcrumbFormatter

Changes

New Files

• src/Tracing/BreadcrumbCollector.php -- Ring buffer collector listening to MessageLogged (skips error+), CacheHit, CacheMissed
• src/Issues/Formatters/BreadcrumbFormatter.php -- Markdown table formatter for breadcrumb data
• tests/Tracing/BreadcrumbCollectorTest.php -- 15 tests covering collection, filtering, ring buffer, config
• tests/Issues/Formatters/BreadcrumbFormatterTest.php -- 7 tests covering formatting, escaping, edge cases

Modified Files

• config/github-monolog.php -- Added breadcrumbs toggle and breadcrumb_limit setting
• src/Tracing/EventHandler.php -- Register breadcrumb event listeners
• src/Tracing/ContextProcessor.php -- Collect breadcrumbs on log time
• src/Issues/TemplateRenderer.php -- Add {breadcrumbs} replacement with BreadcrumbFormatter
• src/Issues/SectionMapping.php -- Add breadcrumbs section mapping and standalone flag pattern
• src/Issues/Formatters/ContextFormatter.php -- Exclude breadcrumbs from generic context
• src/GithubMonologServiceProvider.php -- Add breadcrumbs to context dehydration
• resources/views/issue.md -- Add breadcrumbs section
• resources/views/comment.md -- Add breadcrumbs section

Test plan

• BreadcrumbCollector collects log messages (debug, info, notice, warning)
• BreadcrumbCollector collects cache hit and miss events
• Error/critical/alert/emergency log levels are excluded
• Ring buffer caps at configured limit (keeps latest entries)
• Default limit of 40 applies when not configured
• Collector respects enabled/disabled config toggle
• Breadcrumbs are pushed to Context on collect()
• Chronological order preserved across mixed event types
• BreadcrumbFormatter produces valid markdown table
• Pipe characters in messages are escaped
• Empty breadcrumbs render as empty string (section removed from template)
• Breadcrumbs appear in rendered issue and comment templates
• Breadcrumbs excluded from generic context section
• PHPStan passes with zero errors
• All 303 tests pass

Closes #39

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