docs: explain LISTEN channel identifier quoting

[psh4607]

작업 배경

PGlite already supports PostgreSQL identifier quoting for LISTEN channel names, but the API documentation did not make it clear that names containing hyphens or other special characters must be passed as quoted identifiers.

티켓 및 링크

• GH-747 — Closes Channel name with hyphen does not work #747
• Related identifier case handling: #642

작업 내용

• Replace the basic listen() example with a copy-pastable quoted channel name containing a hyphen and a matching NOTIFY statement.
• Explain PostgreSQL's lowercase folding for unquoted identifiers and the case-preserving, special-character behavior of double-quoted identifiers.
• Clarify that quoted identifiers can subscribe and receive notifications, but per-channel cleanup is not reliable in either PGlite or PGliteWorker; use an unquoted identifier when cleanup is required.
• Keep the change documentation-only; no API behavior, source, tests, or changeset are changed.

테스트

• pnpm --dir docs stylecheck
• pnpm --dir docs typecheck
• VitePress Markdown renderer structural check for the quoted LISTEN/NOTIFY example, the absence of quoted unlisten() guidance, and the cleanup limitation
• git diff --check
• pnpm --dir docs build — blocked before page rendering because this fresh worktree does not contain the generated packages/pglite/dist/index.js workspace artifact; a direct @electric-sql/pglite import fails at the same missing entry point