docs: backport concepts and positioning to 1.2 and 1.1

[killme2008]

What changed

Backport the concepts refresh and related product-positioning corrections to the 1.2 and 1.1 documentation:

• bring the complete 1.2 documentation set from this concepts refresh in line with Nightly, including all nine concept pages, the landing page, Quick Start, the full glossary, and versioned navigation
• backport the same concept structure to 1.1 while keeping version-specific content within its release scope; the 1.1 JSON section documents the experimental JSON type without JSON2, which starts in 1.2
• stop describing GreptimeDB as only a time-series database in the Enterprise overview, installation guide, glossary, and related contributor and operations pages; time-series workloads remain a supported part of the broader data model
• update the versioned sidebars to use Observability 2.0 and wide events, with the matching Chinese label
• preserve the published Wide Events section fragment in both versions

The diagrams remain shared assets under static and are reused by the versioned pages.

Scope

• Documentation versions: 1.2 complete backport; 1.1 version-aware concepts and positioning backport
• Languages: English and Chinese

Verification

• npx --yes markdownlint-cli@0.39.0 -c .markdownlint.yaml on the changed Markdown files
• typos on the changed documentation and navigation files
• JSON parsing for the changed sidebar and localization files
• DOC_LANG=en pnpm check:links
• DOC_LANG=zh pnpm check:links
• rendered sidebar, legacy anchor, JSON/JSON2 scope, and TSDB-positioning checks
• exact Nightly-to-1.2 comparisons for the landing page, Quick Start, and glossary
• git diff --check

Checklist

• I verified the content against the applicable GreptimeDB version.
• I updated the relevant documentation versions and languages, or explained why not.
• I checked changed links and anchors.
• I updated navigation when the document structure changed.

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