feat(summary): add --weekly/-w and --short/-s flags

--weekly (-w): show the summary for the entire week containing the
given day, fetching from Joplin or parsing all tables in the file

--short (-s, repeatable):
  -s alone:       one line per project label + total
  -s --weekly:    per-day project totals with day subtotals
  -ss --weekly:   one line per day with right-aligned date + week total

Add filter_week_sections() to parser.py to split a document into
(date, rows) pairs for a given ISO week. Add print_summary_short(),
print_summary_weekly(), print_summary_weekly_short(), and
print_summary_weekly_totals() to output.py.

.gitignore

@@ -11,3 +11,5 @@ wheels/
 
 # Local config (contains secrets)
 timesheets.toml
+
+timesheets.csv