Docs: expand developer/debugging and tools references

Add extensive documentation and examples across contribution, guides, templates and tools references. Key changes:
- Introduce a Developer Mode & Debugging section (dev_mode flags: trace, keep, pause, breakpoint, logs, dryrun, motd) in CONTRIBUTING.md with usage example.
- Provide a standard update_script() pattern and BookStack example in GUIDE.md to clarify update flow (stop services, backup, deploy, restore, migrate, restart).
- Add new helper entries (BookLore, KaraKeep) and advanced repository helpers (setup_deb822_repo, prepare_repository_setup, cleanup_tool_keyrings) plus utilities (setup_meilisearch, verify_tool_version) in HELPER_FUNCTIONS.md.
- Update install template to suggest PNPM, Java 21 and Meilisearch; update example DB setup notes in AppName-install.sh.
- Add var_diagnostics option and switch var_fuse to boolean/toggle wording in CONFIGURATION_REFERENCE.md; clarify privacy and defaults.
- Adjust example container definitions in UNATTENDED_DEPLOYMENTS.md (container entries and resource values).
- Change storage and flag variables and examples in BUILD_FUNC_USAGE_EXAMPLES.md (ssd-storage, var_fuse/var_tun, etc.).
- Expand TOOLS_FUNC_FUNCTIONS_REFERENCE.md with many setup_* function signatures, environment vars, clarified fetch_and_deploy_gh_release modes/parameters, and additional tool docs (nodejs, php, mariadb_db, postgresql_db, java, uv, yq, meilisearch, composer, build tools).

These updates improve onboarding, debugging guidance, and operational clarity for contributors and maintainers.

docs/contribution/CONTRIBUTING.md

@@ -147,6 +147,30 @@ Verify the PR shows ONLY these 3 files:
 
 ---
 
+# 🛠️ Developer Mode & Debugging
+
+When building or testing scripts, you can use the `dev_mode` variable to enable powerful debugging features. These flags can be combined (comma-separated).
+
+**Usage**:
+```bash
+# Example: Run with trace and keep the container even if it fails
+dev_mode="trace,keep" bash -c "$(curl -fsSL https://raw.githubusercontent.com/community-scripts/ProxmoxVE/main/ct/myapp.sh)"
+```
+
+### Available Flags:
+
+| Flag | Description |
+| :--- | :--- |
+| `trace` | Enables `set -x` for maximum verbosity during execution. |
+| `keep` | Prevents the container from being deleted if the build fails. |
+| `pause` | Pauses execution at key points (e.g., before customization). |
+| `breakpoint` | Allows hardcoded `breakpoint` calls in scripts to drop to a shell. |
+| `logs` | Saves detailed build logs to `/var/log/community-scripts/`. |
+| `dryrun` | Bypasses actual container creation (limited support). |
+| `motd` | Forces an update of the Message of the Day (MOTD). |
+
+---
+
 ## 📚 Pages
 
 - [CT Template: AppName.sh](https://github.com/community-scripts/ProxmoxVE/blob/main/docs/contribution/templates_ct/AppName.sh)