[Docs] Reorganize SeaTunnel onboarding and architecture docs

[yzeng1618]

Purpose of this pull request

This PR reorganizes and expands the SeaTunnel documentation for onboarding, architecture learning, engine usage, and contributor guidance.

refer:https://zread.ai/apache/seatunnel/2-quick-start-installing-and-running-your-first-data-sync-job

Does this PR introduce any user-facing change?

How was this patch tested?

Check list

• If any new Jar binary package adding in your PR, please add License Notice according
  New License Guide
• If necessary, please update the documentation to describe the new feature. https://github.com/apache/seatunnel/tree/dev/docs
• If necessary, please update incompatible-changes.md to describe the incompatibility caused by this PR.
• If you are contributing the connector code, please check that the following files are updated:
  1. Update plugin-mapping.properties and add new connector information in it
  2. Update the pom file of seatunnel-dist
  3. Add ci label in label-scope-conf
  4. Add e2e testcase in seatunnel-e2e
  5. Update connector plugin_config

[DanielLeens]

Hi @yzeng1618, thank you for putting this documentation reorganization together. I pulled the PR locally and reviewed the full diff against the current dev baseline rather than only reading the PR description.

Local review branch: seatunnel-review-10785
Head reviewed: 350e5dd318e29a20f74bbe9e00e6ba977fb65e7f
Baseline: upstream/dev merge-base ae8b96caeff98ece65c1cd63d0f88c9ccffbfd5c

What this PR improves

Before this PR, a new user or new contributor had to jump between several scattered pages to understand the first-run path, engine choice, job configuration shape, architecture concepts, and developer entry points.

This PR adds and wires a clearer onboarding path across:

• Getting Started overview and job configuration guide
• Architecture overview, core API, CDC pipeline, type system, plugin discovery, and transform system pages
• Flink and Spark translation layer pages
• Source and Sink connector development pages
• REST API and Web UI operational entry page

In plain terms: this makes the docs feel much more like a guided path instead of a set of separate islands.

Runtime / documentation path checked

This PR does not change SeaTunnel runtime code. The real path it changes is the documentation publish and navigation path:

docs source in this PR
  -> docs/sidebars.js
      -> Architecture adds configuration/core API/CDC/type/plugin discovery entries
      -> Getting Started adds overview and job-configuration-guide
      -> Zeta Engine adds rest-api-and-web-ui
      -> Developer adds contribution-path/source/sink connector development

website sync path
  -> tools/documents/sync.sh
      -> copies docs/en, docs/zh, and docs/sidebars.js into the Docusaurus website tree

user reading path
  -> Getting Started Overview
      -> choose Zeta / Flink / Spark
      -> Quick Start With SeaTunnel Engine or engine-specific quick starts
      -> Job Configuration Guide
      -> Source / Transform / Sink docs
      -> Architecture and Developer pages when deeper context is needed

I also checked the technical references in the new pages against the repository:

• CDC references such as IncrementalSource, IncrementalSourceEnumerator, and IncrementalSourceReader exist under seatunnel-connectors-v2/connector-cdc/connector-cdc-base.
• Flink translation references such as FlinkSource, FlinkSourceReader, and FlinkSourceEnumerator exist under seatunnel-translation/seatunnel-translation-flink.
• Spark translation references such as SparkSink and SparkDataSourceWriter exist under seatunnel-translation/seatunnel-translation-spark.
• The quick-start use of FieldMapper is valid because seatunnel-transforms-v2.jar is included in the binary distribution assembly.

Local checks performed

• git fetch upstream pull/10785/head:seatunnel-review-10785 --force: passed.
• git diff --stat upstream/dev...HEAD: 67 files, +6425/-259, all in docs/sidebar scope.
• git diff --check upstream/dev...HEAD: passed, no whitespace errors found.
• Sidebar validation: all 110 explicit doc ids in docs/sidebars.js resolve under docs/en.
• Modified-doc relative link validation: no missing relative Markdown links found in the changed docs.
• Code-reference spot check: key directories and classes named by the new architecture/developer pages exist in the local source tree.
• GitHub checks observed: Build, Notify test workflow, and labeler are all passing.

I did not run a local Docusaurus build because this repository contains the docs source and sync script, not the website package itself. I also did not run Maven tests because this PR is documentation-only and does not touch runtime code.

Review findings

No blocking issue was found.

Compatibility assessment:

• API: no impact
• Configuration options/defaults: no impact
• Protocols: no impact
• Serialization/state format: no impact
• Runtime behavior: no impact
• Historical compatibility: fully compatible

Side-effect assessment:

• No CPU, memory, GC, network, locking, concurrency, retry, idempotency, or resource-release impact, because the PR does not change runtime code.
• The only practical side effect is a larger docs surface area, and the navigation/link checks look healthy.

Merge conclusion

Conclusion: can merge

Blocking items:

• None.

Non-blocking suggestions:

• Please keep the website-side dead-link / Docusaurus build checks in place after merge. The current PR is fine from this review, but broad documentation reorganizations benefit from continuous link validation as the docs evolve.

Overall evaluation:

This is a focused and useful documentation-architecture improvement. It makes the project friendlier for new users and contributors while staying aligned with the actual SeaTunnel Source -> Transform -> Sink model, CDC flow, plugin discovery path, and engine translation modules. Nice work.

[davidzollo]

+1
Great job. Thank you very much for your contribution to the documentation, which is of great importance to the users and developers of the SeaTunnel community. Thank you again for your significant contribution to the community!

[corgy-w]

good pr