Add ToolJet + Couchbase integration tutorial (#96)

* Add ToolJet + Couchbase tutorial: Build an Airline Dashboard

Step-by-step tutorial covering all 6 Couchbase operations in ToolJet
(CRUD, SQL++, FTS) using the travel-sample dataset. Includes setup
paths for both Capella and self-managed clusters.

* fix: address review comments on tutorial

- Fix frontmatter tags to use allowed values (Data API, Connector,
  SQL++ (N1QL), FTS, REST API) and stay within the 6-tag limit
- Remove 0.0.0.0/0 suggestion from Capella setup, add security note
  guiding users to find their actual IP instead
- Add parameterized query example ($country) in Step 3 demonstrating
  safe SQL++ parameter binding via the args field
- Remove parameterized queries from "Next Steps" since now covered
- Pin Docker images to specific versions (couchbase:7.6.2,
  tooljet/tooljet-ce:v3.16.0-LTS) for tutorial reproducibility

* fix: address Prajwal's review feedback on tutorial

- Add Overview section at top of tutorial
- Add anchor links in Prerequisites to Couchbase Cluster Setup and
  ToolJet Setup sections
- Add Couchbase docs links for loading travel-sample and allowing IPs
  in Capella
- Clarify self-managed Data API endpoint is server hostname/IP, not
  always localhost
- Add ToolJet self-hosted setup docs link
- Remove redundant connection details table in Step 2, replace with prose
- Remove duplicate Capella/Self-Managed sub-sections inside Step 2
- Move FTS index creation into Prerequisites section with cross-reference
  in Step 9

* feat: embed screenshots and add parameterized query example

- Add 8 screenshots from ToolJet docs to the tutorial directory
- Embed screenshots at appropriate steps: connection config, operations
  dropdown, SQL++ query, Get/Create/Update/Delete Document, FTS Search
- Screenshots are co-located with the markdown file per repo convention

* fix: correct screenshot placements and add clarifying captions

- Move query-v2.png to parameterized query section (it shows args/options,
  not the basic listAirlines query)
- Add captions noting _default scope/collection in CRUD screenshots
  should be replaced with inventory/airline
- Add caption noting hotel-index in fts-search-v2.png should be
  replaced with airline-name-index

* docs: reorganize tooljet tutorial images + add dashboard/modal screenshots

Respond to review feedback requesting a dashboard/modal screenshot, and
clean up the image layout for future maintenance.

- Add 4 new screenshots captured against a live ToolJet + Capella setup:
  * capella/data-api-enabled.png — Connect → Data API page with endpoint URL
  * setup/marketplace-install.png — Couchbase plugin card in Marketplace
  * dashboard/airlines-table-populated.png — Table bound to listAirlines
  * dashboard/airline-details-modal.png — Modal showing getAirline result
- Move 8 existing screenshots into images/{setup,operations}/ subfolders
  with descriptive names (e.g. get-doc.png -> operations/get-document.png)
- Update all image references in the tutorial markdown accordingly

* docs: blur Data API endpoint URL in Capella screenshot

Author: teetangh