v1.0.1-beta.3

feat(release): publish VS Code extension VSIXes from release.yml

Adds a publish-vscode-extension job: fetches the tagged release's own
archives (not the ephemeral build-release-assets artifacts, so a
workflow_dispatch re-publish works long after the original run's 1-day
artifact retention expires), packages all 8 platform VSIXes via the
existing package-platforms.mjs version policy, publishes them with
vsce --skip-duplicate for idempotent re-runs, and attaches the VSIXes
plus checksums to the GitHub release. Isolated with
continue-on-error: true, same as publish-npm/publish-mcp-registry.

Adds a workflow_dispatch fallback (tag input) scoped to just this job;
build-release-assets (and everything that transitively needs it) is
gated to the release event only, so a manual dispatch never re-runs
the binary build/upload path.

ISSUE-78

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>