Condenser: build.sh converter with --help and subcommands

[mdeguzis]

Add a build.sh at the branch root that does the makefile-style jobs through a case statement, with full --help. It converts our plugin source into the two files condenser ships (frontend.js + backend.mjs).

Subcommands to start: help, dev (run against sibling condenser-app), shim (generate frontend.tsx/backend.ts entry from our src), build (esbuild to dist), package (zip the two files), clean. Keep real logic in the script, not inline, and reuse functions across subcommands.

Reference: condenser-plugin/scripts/build.mjs and dev.mjs show the esbuild + sibling-resolution pattern.

[mdeguzis]

Scaffold landed on the condenser branch. build.sh dispatcher is in with help/deps/doctor/dev/build/package/clean, real logic in condenser/scripts/*.mjs. ./build.sh build bundles condenser/frontend.tsx + backend.ts to dist/frontend.js + backend.mjs via esbuild, React aliased to the sibling condenser-app so we do not bundle our own copy. package zips exactly the two files the loader allows. Still a stub surface; the converter that pulls our real tabs and shared lib is the next layer.