DOCS-1772 - Rename Cloud SIEM to SIEM sitewide

[JV0812]

Purpose of this pull request

This pull request renames the product from "Cloud SIEM" to "SIEM" across the Help site, per DOCS-1772, ahead of new product announcements in August.

• Replaces ~2,500 occurrences of "Cloud SIEM" (and its lowercase/hyphenated path/tag forms) with "SIEM" across doc content, titles, sidebar labels, keywords, and metadata — including the global sitewide meta keywords tag and the homepage feature grid.
• Renames 11 files and 2 directories whose paths baked in "cloud-siem" (affecting 48 published URLs), using git mv to preserve history.
• Adds 48 new 301 redirect entries to cid-redirects.json for the renamed URLs, and updates existing redirect entries that previously pointed at the old cloud-siem paths so they don't double-hop.
• Updates internal .claude/commands/ skill docs and the Japanese i18n mirror for consistency (including syncing a sidebar-label-derived i18n translation key).

Intentionally left untouched — these hold literal API/config values rather than display text, and I couldn't verify the backend accepts a renamed value:

• docs/send-data/.../cse-aws-ec-inventory-source.md — one inline schemaRef JSON value ({"type":"Cloud SIEM AWS EC2 Inventory"})
• static/files/c2c/cse-aws-ec-inventory/example{1,2}.{json,tf} — the matching downloadable Terraform/JSON examples

Verified with a full yarn build (twice) — no broken links or warnings.

Select the type of change

• Minor Changes - Typos, formatting, slight revisions
• Update Content - Revisions, updating sections
• New Content - New features, sections, pages, tutorials
• Site and Tools - .clabot, version updates, maintenance, dependencies, new packages for the site (Docusaurus, Gatsby, React, etc.)

Ticket (if applicable)

https://sumologic.atlassian.net/browse/DOCS-1772