PHLEGM v6 shared Compiler diagnostic logging checkpoint

- Canonical external Install-and-Compile initiation creates the first Phoenix timestamp and a visible `PHLEGM-Compiler-Run-<timestamp>/` staging directory; there is no leading dot.
- The bootstrap transcript is closed before the long-lived browser Compiler UI starts so no open bootstrap log handle can block ZIP finalization.
- Compiler-UI diagnostics are data-driven with diagnostics.bundleScope=`build-completion` and removeRunDirectoryAfterBundle=true.
- The first Compile uses the bootstrap timestamp. Each later Compile while the same UI remains open receives a fresh Phoenix timestamp and its own run directory.
- Build scripts receive the active build timestamp through diagnostics.parentBuildTimestampSwitch, so build stdout/stderr and matching project compiler/package/checksum logs share that timestamp.
- As soon as a build passes, fails, or is cancelled, the Compiler UI collects matching project logs and creates `PHLEGM-v6-Compiler-Logs-<timestamp>.zip` immediately; closing the Compiler UI is not required.
- After a successful ZIP finalization the transient run directory is removed. If ZIP creation/removal fails, the visible run directory is retained for diagnosis.
- Completed stdout/stderr are retained in memory so the browser UI can continue displaying the completed build after its staging directory has been removed.
- A later build from the still-open Compiler UI starts a new timestamped diagnostic run without overwriting the prior log bundle.
- Early bootstrap/no-build failure paths still fall back to bootstrap-side bundling.
- Running executables under the final non-destructive install path are still terminated before UI start and before each build.
