Retire every deprecation shim

[JSONbored]

Problem: Once the grace/deprecation windows from the npm package rename, the self-host image rename, the config-filename dual-read, the environment-variable dual-read, and the MCP tool aliases have all elapsed, the old names are still live in code and infrastructure.

Area: Cleanup

Proposal: Remove active maintenance of the old npm package names, stop publishing the old container image tag, drop legacy config-filename and environment-variable dual-read support, and remove the MCP tool aliases. Add a single changelog entry documenting the rebrand.

Deliverables:

• All shims and aliases removed.
• One changelog entry.

Acceptance criteria:

• No code path references the old names, except the changelog entry itself.
• The full test suite passes with legacy-name test cases removed or updated.

Test scenarios:

• Full test-suite run after removal, confirming no regression.

Resources:

• The changelog file.

Boundaries:

• Only proceed once every individual grace period named in the earlier steps has actually elapsed.
• This changelog edit is a deliberate, maintainer-authored exception to the standing "never hand-edit the changelog in a normal PR" rule, since this isn't a normal contributor PR.

---

Part of #4761.

[linear-code]

JSO-3449