Set up prettier-plugin-organize-imports

[Arman-Luthra]

What are you adding in this PR?

Closes #540.

This sets up prettier-plugin-organize-imports as requested in the issue and the linked review discussion on #529, so pnpm format now sorts imports and removes unused ones.

The work is split into two commits so the mechanical diff is reviewable on its own, as suggested in that discussion:

1. Setup: adds prettier-plugin-organize-imports@4.3.0 to the workspace root devDependencies, registers it in .prettierrc.json, and adds editor.codeActionsOnSave: { "source.organizeImports": "explicit" } to .vscode/settings.json. Peer requirements are satisfied by the repo's existing prettier ^3.0.0 and typescript ^5.9.0.
2. Reformat: runs pnpm format across the workspace, organizing imports in 473 files.

An empty changeset is included, since this is tooling-only and changes no published package behavior.

One risk with this plugin is that it can drop imports that exist only for side effects. I checked the formatted scope for those: the single side-effect-only import (test-setup in LiquidDocTagHoverProvider.spec.ts) survived the reformat, and the type-check plus full test suite pass covers the rest.

What's next? Any followup issues?

None. If this sits for a while before merge, the mechanical commit may need a fresh rebase to avoid conflicts; happy to redo it on request.

Tophatting

• pnpm format:check passes after the reformat, so the output is stable and idempotent
• pnpm build:ts and pnpm type-check pass across all packages with zero errors
• pnpm vitest run passes the full suite: 296 test files, 1882 passed, 1 skipped
• pnpm lint reports 17 pre-existing problems in vscode-extension that reproduce identically on an unmodified checkout, so they are unrelated to this change

Before you deploy

• I included a changeset (empty, since this is tooling-only with no published package behavior change)