DO-1867: refresh repo docs and adopt org-shared community files

[TheOrangePuff]

Description of the proposed changes

Refreshes the repository's developer-facing documentation:

• CLAUDE.md — corrects inaccurate guidance (the install command, the package layout, the dist/ path, etc.) and brings it in line with how the repo actually works (Yarn 4 / Corepack workspaces, nx affected:* mirroring CI, Changesets release flow with the team's "confirm with the user before writing a changeset" rule, peer-dep contract for aws-cdk-lib/constructs, ESLint module-boundary allowlist).
• README.md — adds an "Adding a new package" section under Contributing covering the package skeleton, the constructs-table update, and the changeset for the initial release. Includes a > [!IMPORTANT] callout that the first publish must be done manually because our release workflow uses npm OIDC trusted publishing, which can only push new versions to packages that already exist on npm — it cannot create the package itself.
• CONTRIBUTING.md, CODE_OF_CONDUCT.md, .github/pull_request_template.md — removed in favour of the org-shared equivalents in aligent/.github. GitHub will fall back to those automatically.

Notes to reviewers

• Three commits, each scoped to one logical change, so the diff is easy to read commit-by-commit.
• No code or workflow changes — docs/community-files only.

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[aaronmedina-dev]

LGTM