fix: preserve an existing non-PortOS ecosystem.config.cjs during PM2 standardization

[atomantic]

Problem

Running PM2 standardization on an app unconditionally overwrote ecosystem.config.cjs. If the app already had a hand-authored PM2 config, standardizing silently replaced it — losing its custom ports and settings. (Hit in practice: a work app's carefully-tuned local-dev config, with non-default ports wired into its scripts, README, and OIDC callback, got clobbered by the standardizer's generic template.)

Fix

Make the standardizer respect an existing config it didn't create:

• Preserve by default. If ecosystem.config.cjs exists and does not carry PortOS's generated-header marker (i.e. it's user-authored or another tool's), it is left untouched. Only a file PortOS previously generated (marker present) is regenerated — the normal re-standardize flow still works.
• Don't strip its ports either. When the config is preserved, the coupled .env / vite.config stray-port removal is skipped — pulling ports out of those only makes sense once PortOS's generated ecosystem owns them.
• Explicit opt-in to overwrite. A new overwriteEcosystem flag forces regeneration of a user-authored config. Exposed on the /api/standardize/apply request body and both standardize:start / app:standardize socket events (validated, optional, default false).
• Fails safe. Provenance is re-read from disk at apply time (not trusted from the stale analyze plan); if the file exists but can't be read, it's preserved rather than clobbered.
• Detection reuses a single PORTOS_ECOSYSTEM_MARKER constant that also stamps generated output, so the stamp and the check can't drift. Results now report filesPreserved alongside filesModified, surfaced through the flow + socket events.

Tests

• New real-FS applyStandardization cases (temp dirs): preserves a user-authored config by default; regenerates a PortOS-generated one; overwrites when overwriteEcosystem: true; writes fresh when none exists; leaves .env stray ports alone when preserving but still strips them when regenerating.
• Updated / added runStandardizeFlow cases for the opt-in forwarding and the filesPreserved passthrough.
• Full server suite green (789 files, 15,769 tests).

Changelog

Added a ## Fixed entry to .changelog/NEXT.md.