Improve README readability

[Widthdom]

Summary

• replace the long bilingual README sections with compact tables and focused examples
• keep the status field groups visible as a compatibility index while linking detailed contracts to the user and developer guides
• remove duplicate badges from both language sections of the user guide

Why

The README had accumulated detailed command and contract prose that duplicated the dedicated guides. This made the project overview difficult to scan and blurred the boundary between introductory and reference documentation.

Impact

The README is reduced from 1,037 lines to 391 lines while preserving its English and Japanese sections, installation entry points, representative commands, supported surfaces, documentation map, status field index, release verification, and license guidance.

Detailed behavior remains available through links to USER_GUIDE.md and DEVELOPER_GUIDE.md.

Validation

• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --framework net8.0 --filter 'FullyQualifiedName~DocumentationDriftTests|FullyQualifiedName~LicensePolicyTests' --no-restore --nologo — 17 passed
• git diff --check
• cdidx outline README.md --json --kind heading --limit 100 --max-json-bytes 32768 — 26 bilingual headings recognized
• cdidx status --check --json — workspace matched and readiness checks passed

Documentation and changelog

• updated README.md and USER_GUIDE.md
• no changelog fragment was added because this is documentation-only restructuring with no CLI, API, MCP, LSP, or runtime behavior change

Follow-ups

None.