add incremental refresh + cooldown to -likes mode

After backfill completes for a blog, -likes can now pick up only newer
likes instead of being a one-shot pull. Tracks a per-blog
liked_timestamp high-water mark and stops the refresh walk once it
crosses the stored mark. A configurable cooldown (LikesRefreshCooldownDays,
default 7) gates which blogs are re-checked on each run. -force bypasses
the cooldown.

The migration adds three columns to Blogs (LikesNewestTimestamp,
LikesLastRefreshed, LikesLastNewCount) and does a one-time reset of all
likes tracking state so the new high-water mark starts from a clean
baseline. Existing ByLikes posts remain; the UNIQUE constraint absorbs
re-inserts during the first re-backfill.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

URLNotesGrabberCORE/appsettings.json

@@ -11,7 +11,8 @@
     "ContainsList": "zombaee,zomb-eh,ahzombae,thebugandme,lovingbabybug,h4rdspot",
     "PostIDToExclude": "730084470076686336,726309940037287936,639974102120235008,184045126218",
     "EnableFileLogging": false,
-    "LogTraversalRecordImports": false
+    "LogTraversalRecordImports": false,
+    "LikesRefreshCooldownDays": 7
   },
   "TumblrApi": {
     "ConsumerKey": "PtsBCGumcsgihyynxUh8b47Jfmi7uXhEIOU46bmhdsUSJ5mEP3",