Avoid redundant dev-server generation and batch watcher updates.

[koculu]

Summary

Avoid redundant dev-server generation and batch watcher updates

Changes

Serve mode now skips CSS generation when styles haven’t changed and shares content discovery and navigation refresh across each watcher event batch. This reduces repeated work when Windows emits bursts of file notifications.

• Track style revisions without comparing generated CSS; identical declarations leave the revision unchanged.
• Preserve concurrent style changes for the next request by recording the revision associated with the generated CSS snapshot.
• Log each successfully generated CSS file with its theme and output path.
• Stop queued watcher work during shutdown and clear batch caches after failures.
• Disable sitemap.xml and robots.txt generation in serve mode, including --full-render and config reloads. Build and publish retain their configured behavior.

Validation:

TypeScript checks passed, alongside 63 incremental-builder and dev-server tests.
Added regression coverage for concurrent CSS changes, watcher batches, additions and deletions, cancellation, failure recovery, and disabled dev sitemap/robots generation.