fix: preserve workflow data during serialization (Issue #517) (#519)

Fixed a critical bug where workflow mutation data was corrupted during
serialization to Supabase. The recursive toSnakeCase() function was
converting nested workflow data, mangling:
- Connection keys (node names like "Webhook" → "_webhook")
- Node field names (typeVersion → type_version)

Solution: Replace recursive conversion with selective mutationToSupabaseFormat()
that only converts top-level field names to snake_case while preserving
nested workflow data exactly as-is.

Impact:
- 98.9% of workflow mutations had corrupted data
- Deployability rate improved from ~21% to ~68%

Changes:
- src/telemetry/batch-processor.ts: New selective converter
- tests/unit/telemetry/batch-processor.test.ts: 3 new regression tests

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Romuald Członkowski <romualdczlonkowski@MacBook-Pro-Romuald.local>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,43 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [2.31.4] - 2026-01-02
+
+### Fixed
+
+**Workflow Data Mangled During Serialization: snake_case Conversion (Issue #517)**
+
+Fixed a critical bug where workflow mutation data was corrupted during serialization to Supabase, making 98.9% of collected workflow data invalid for n8n API operations.
+
+**Problem:**
+The `toSnakeCase()` function in `batch-processor.ts` was applied **recursively** to the entire mutation object, including nested workflow data that should be preserved exactly as-is:
+
+- **Connection keys mangled**: Node names like `"Webhook"` became `"_webhook"`, `"AI Agent"` became `"_a_i _agent"`
+- **Node field names mangled**: n8n camelCase fields like `typeVersion`, `webhookId`, `onError` became `type_version`, `webhook_id`, `on_error`
+
+**Root Cause:**
+```javascript
+// Old code - recursive conversion corrupted nested data
+result[snakeKey] = toSnakeCase(obj[key]); // WRONG
+```
+
+**Solution:**
+Replaced recursive `toSnakeCase()` with selective `mutationToSupabaseFormat()` that:
+- Converts **only** top-level field names to snake_case (for Supabase columns)
+- Preserves all nested data (workflow JSON, operations, validations) **exactly as-is**
+
+```javascript
+// New code - preserves nested workflow structure
+for (const [key, value] of Object.entries(mutation)) {
+  result[keyToSnakeCase(key)] = value; // Value preserved as-is
+}
+```
+
+**Impact:**
+- Workflow mutation data now maintains n8n API compatibility
+- Deployability rate improved from ~21% to ~68%
+- Added 3 regression tests to prevent future occurrences
+
 ## [2.31.3] - 2025-12-26
 
 ### Fixed