docs: Add comprehensive TROUBLESHOOTING.md guide

[jadonamite]

### Overview
This PR creates a new, extensive `TROUBLESHOOTING.md` guide for the repository.

Currently, the repository lacks a centralized resource for debugging common runtime errors. This leads to repetitive issues regarding syncing, hardware requirements, and Docker misconfigurations. This PR fills that gap with a structured guide covering the most frequent operator pain points.

###Motivation & Context
Node operators frequently encounter issues that are not bugs in the code, but environmental or configuration constraints.
* **Context Deadline:** Users confuse disk bottlenecks with network errors.
* **JWT Errors:** Docker volume mapping often leads to auth failures between `op-node` and execution clients.
* **L1 Connection:** Derivation failures due to poor L1 RPC quality.

Providing a centralized "Self-Help" document will reduce the support burden on maintainers and discord moderators.

###  Content Included
The new guide covers three main categories:
1.  **Syncing & Performance:**
    * Detailed breakdown of the "Context Deadline Exceeded" error (IOPS vs Latency).
    * Snap sync behaviors ("Healing").
2.  **Configuration & Connectivity:**
    * Engine API (JWT) troubleshooting.
    * L1 RPC requirements and common failures.
    * P2P discovery (ports/firewalls).
3.  **Docker & Operations:**
    * Permission denied errors on data volumes.

### Checklist
- [x] Created `TROUBLESHOOTING.md`
- [x] Covered hardware/IOPS requirements extensively.
- [x] Included specific log signatures for easy `Ctrl+F` searching.

[cb-heimdall]

🟡 Heimdall Review Status

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Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1