feat: captain custom tools v1 (#13890)

# Pull Request Template

## Description

Adds custom tool support to v1

## Type of change
- [x] New feature (non-breaking change which adds functionality)


## How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide
instructions so we can reproduce. Please also list any relevant details
for your test configuration.

<img width="1816" height="958" alt="CleanShot 2026-03-24 at 11 37 33@2x"
src="https://github.com/user-attachments/assets/2777a953-8b65-4a2d-88ec-39f395b3fb47"
/>

<img width="378" height="488" alt="CleanShot 2026-03-24 at 11 38 18@2x"
src="https://github.com/user-attachments/assets/f6973c99-efd0-40e4-90fe-4472a2f63cea"
/>

<img width="1884" height="1452" alt="CleanShot 2026-03-24 at 11 38
32@2x"
src="https://github.com/user-attachments/assets/9fba4fc4-0c33-46da-888a-52ec6bad6130"
/>



## Checklist:

- [x] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>

app/javascript/dashboard/i18n/locale/en/integrations.json

@@ -807,6 +807,7 @@
     "CUSTOM_TOOLS": {
       "HEADER": "Tools",
       "ADD_NEW": "Create a new tool",
+      "SOFT_LIMIT_WARNING": "Having more than 10 tools may reduce the assistant's reliability in selecting the right tool. Consider removing unused tools for better results.",
       "EMPTY_STATE": {
         "TITLE": "No custom tools available",
         "SUBTITLE": "Create custom tools to connect your assistant with external APIs and services, enabling it to fetch data and perform actions on your behalf.",
@@ -837,11 +838,18 @@
         "SUCCESS_MESSAGE": "Custom tool deleted successfully",
         "ERROR_MESSAGE": "Failed to delete custom tool"
       },
+      "TEST": {
+        "BUTTON": "Test connection",
+        "SUCCESS": "Endpoint returned HTTP {status}",
+        "ERROR": "Connection failed",
+        "DISABLED_HINT": "Testing is only available for endpoints without templates or request bodies."
+      },
       "FORM": {
         "TITLE": {
           "LABEL": "Tool Name",
           "PLACEHOLDER": "Order Lookup",
-          "ERROR": "Tool name is required"
+          "ERROR": "Tool name is required",
+          "MAX_LENGTH_ERROR": "Tool name must be {max} characters or fewer"
         },
         "DESCRIPTION": {
           "LABEL": "Description",