feat(collect): let --force ignore the re-collect cooldown

--collect 1 <blog> returned an empty worklist whenever the periodic
re-queue branch was still inside its 3-day window, with no way to ask
for the re-collect early. GetPosts now composes that age predicate
conditionally, and the existing global --force flag - already "ignore
cooldown" for --likes - drives it.

Only the age gate drops: NotFound = 0, the IsActive filter and the blog
scoping still apply. The flag is a no-op for mode 0, which re-collects
every post regardless, and says so rather than pretending to act.

Co-Authored-By: Claude Opus 5 <[email protected]>

.github/copilot-instructions.md

@@ -31,7 +31,7 @@ dotnet run -- --test [blogname] [postID]  # Test API for specific post
 - `--test [blogname] [postID]`: Test API note collection
 - `--posts`: Export post blogs to file
 - `--blogs`: Export blog list to file
-- `--collect [0|1] [datetime] [blogname]`: Collect notes for posts in DB. Optional `blogname` restricts the run to one blog (exact match), e.g. `--collect 1 zomb-eh`
+- `--collect [0|1] [datetime] [blogname]`: Collect notes for posts in DB. Optional `blogname` restricts the run to one blog (exact match), e.g. `--collect 1 zomb-eh`. Add `--force` to ignore the periodic re-collect cooldown so already-collected posts are re-queued immediately (mode 1 only)
 - `--blogsR`: Export reply blogs to file
 - `--blogsO [start] [stop]`: Export blogs within range