rebrand: publish npm package as open-tag and update the release flow

[liuchao-001]

Part of the OpenTag rebranding migration decided by @liuchao-001 on 2026-08-11. Durable decisions/constraints are recorded in the Context Tree (system/opentag-migration.md, tree PR agent-team-foundation/first-tree-context#915). Related brand decisions: customer/marketing/rebranding.md.

Scope

The npm package name open-tag is registered. Update the publish pipeline to release under open-tag.

• Update package name, bin entries, and release automation (CI publish jobs, provenance, release channels).
• Decide and implement the transition for the old package name: final deprecation release pointing to open-tag (npm deprecate), so existing installs/self-update paths do not silently strand.
• Verify the daemon/CLI self-update path works across the rename (see prior ENOTEMPTY self-update issues for the failure mode).

Acceptance

• npm install -g open-tag installs a working CLI; release CI publishes to open-tag.
• Old package shows a deprecation notice pointing to open-tag; documented upgrade path for existing users.