* fix(build): clean stale outputs before tsc --build to prevent TS5055
Run `tsc --build --clean` before `tsc --build` in build_package.js so a
stale tsconfig.tsbuildinfo (e.g. after a version bump, branch switch, or
a prior `npm ci` prepare) cannot collide with composite project
references emitting back into packages/core/dist.
Closes#4447
* fix(build): scope clean step to current package only
Replace `tsc --build --clean` with direct `rmSync` of `dist` and
`tsconfig.tsbuildinfo`. `tsc -b --clean` walks project references, so
when scripts/build.js builds packages in dependency order, cleaning
from a downstream package (e.g. cli) would also wipe upstream outputs
(core, acp-bridge, channels) that were just built — a major perf
regression.
Spotted by Copilot review on #4453.
