fix(backtest,multi-vm): handle MT5 relaunch, per-VM healthchecks, orphan sweep

[Marinski]

Five bug fixes that surfaced while running backtests on a multi-terminal deployment: backtests on terminals that had in fact run them were being reported as failed, and the container healthcheck was permanently red, masking a genuine outage.

What and why

Backtest reliability

• MT5 self-relaunch on update. When a LiveUpdate is pending, the launched terminal process exits 0 within seconds and MT5 relaunches itself to run the real test. The job was failed as "Report not generated" even though a valid report was written minutes later. The runner now waits for the replacement process and its run, bounded by the existing job timeout; a run long enough to be a real backtest is not an update restart and still fails immediately.
• INI values treated as literals. ConfigParser interpolation rejected bare % characters in symbols, report names and percentage inputs, causing a spurious 400 on submission. RawConfigParser is now used on both the read and write sides, matching how MT5 treats these values.

Multi-VM healthchecks

• check_health.py probed every port in config.yaml. On a multi-VM install each VM reported the other VM's terminals DOWN and the container sat permanently unhealthy, making a genuine failure indistinguishable from standing noise (observed: a 25,000+ failing streak while all local terminals were serving). It now applies the same per-VM group filter the launcher uses, with a fallback to no-filter if the import fails.
• healthcheck.sh had the same bug — it grepped every port: in config.yaml. It now filters by the per-VM group file docker-compose already bind-mounts, using awk since the container image has no python. No group file means no filter, preserving single-VM behaviour.

Startup performance

• sweep_orphans() parsed every job file at boot. On a large shared backtest-jobs dir this took ~2.5 minutes per process, multiplied by the number of processes starting at boot — all to mark in-flight jobs failed. It now inspects only state files touched within BACKTEST_SWEEP_LOOKBACK, and a new prune_old_jobs() retires completed/failed jobs older than BACKTEST_JOB_RETENTION, gated by a shared marker so only one process scans per interval. Both run in a background daemon thread so boot never blocks, and writes are atomic (tmp+rename) so concurrent sweepers never see truncated files.

Testing

• Unit suite updated to cover relaunch handling, INI literals, per-VM healthcheck filtering, and job sweep/prune. 241 tests pass.
• Lint clean.