feat(aw): add Japanese documentation auto-sync workflows

[viktorkombov]

Closes #139

Ports the Japanese translation agentic workflow from igniteui-docfx and
igniteui-xplat-docs to this Astro monorepo.

Changes

• Added .github/workflows/sync-jp-docs-angular.md — gh-aw agent for
  docs/angular. Triggers on push to master when English content changes,
  translates to Japanese, and opens a PR. Adapted for MDX files, JSON TOC
  structure, and the new content paths.
• Added .github/workflows/sync-jp-docs-xplat.md — same for
  docs/xplat. Adds xplat-specific rules for <PlatformBlock> components
  and {Token} placeholder preservation.
• Added .github/aw/actions-lock.json — pinned action SHAs required by
  the gh-aw compiler.
• Added .github/README.md — documents how to edit workflows, run
  gh aw compile, and which secrets need to be provisioned.
• Removed docs/angular/.github/workflows/sync-jp-docs.{md,lock.yml} and
  docs/angular/.github/aw/ — these were in a subfolder GitHub Actions never
  reads, referenced outdated paths, and are superseded by the root-level files.

Follow-up required

• Run gh aw compile once locally (needs gh extension install github/gh-aw)
  and commit the generated *.lock.yml files before the workflows can execute.
• Add COPILOT_GITHUB_TOKEN (required) and GH_AW_GITHUB_TOKEN (recommended)
  to repo secrets — same values as in igniteui-docfx / igniteui-xplat-docs.
• Once vnext is created, update the trigger branch from master to vnext
  in both workflow .md files and recompile.

[Copilot]

Pull request overview

Ports the Japanese documentation auto-sync agentic workflows (gh-aw) into the repo’s root .github/ area so they can translate updated English docs and open PRs for docs/angular and docs/xplat.

Changes:

• Added gh-aw workflow sources for syncing JP docs for Angular and xplat doc trees.
• Added a pinned actions lockfile for gh-aw compilation/execution.
• Added contributor documentation for compiling/updating agentic workflows and required secrets.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

File	Description
.github/workflows/sync-jp-docs-xplat.md	Adds xplat JP sync agent workflow source (MDX + token preservation rules).
.github/workflows/sync-jp-docs-angular.md	Adds Angular JP sync agent workflow source (includes TOC-based filtering logic).
.github/README.md	Documents gh-aw workflow editing/compiling and required secrets.
.github/aw/actions-lock.json	Pins action SHAs for gh-aw compilation.

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