Add ~ marker to exclude entries from CSV export

Prefix the project name or note column with ~ to mark an entry as
count-but-don't-export. Marked entries are included in summary and
status totals but omitted from all csv output (both --raw and
aggregated, single-day and weekly).

  | 09:00 | 17:00 | 8:00 | ~Leave |  | Day off  |
  | 09:00 | 17:00 | 8:00 |  Leave |  | ~Day off |

The ~ is stripped from whichever field carries it before any
downstream processing, so project map resolution is unaffected.

Implementation:
- parse_table sets skip_csv=True on marked rows and strips the ~
- new filter_skip_csv() helper in parser.py
- to_csv_entries() skips skip_csv rows
- _cmd_csv calls filter_skip_csv() before aggregate_rows()

tests/test_parser.py

@@ -8,6 +8,7 @@ from timesheets.parser import (
     detect_has_duration_column,
     extract_table_blocks,
     filter_rows_by_date,
+    filter_skip_csv,
     parse_document,
     parse_table,
     resolve_overlaps,
@@ -351,6 +352,127 @@ class TestBuildDescription:
 # ---------------------------------------------------------------------------
 
 
+# ---------------------------------------------------------------------------
+# skip_csv marker (~project)
+# ---------------------------------------------------------------------------
+
+
+class TestParseTableSkipCsv:
+    _LINES = [
+        "| Start | End   | Duration | Project | Story | Note     |",
+        "|-------|-------|----------|---------|-------|----------|",
+        "| 09:00 | 17:00 | 8:00     | ~Leave  |       | Day off  |",
+        "| 09:00 | 10:00 | 1:00     | work    | st    |          |",
+    ]
+
+    def test_tilde_sets_skip_csv(self):
+        rows = parse_table(self._LINES)
+        leave = next(r for r in rows if "Leave" in r["project"])
+        assert leave["skip_csv"] is True
+
+    def test_tilde_stripped_from_project(self):
+        rows = parse_table(self._LINES)
+        leave = next(r for r in rows if r.get("skip_csv"))
+        assert leave["project"] == "Leave"
+
+    def test_tilde_with_space_stripped(self):
+        lines = [
+            "| Start | End   | Duration | Project  | Story | Note |",
+            "|-------|-------|----------|----------|-------|------|",
+            "| 09:00 | 17:00 | 8:00     | ~ Leave  |       |      |",
+        ]
+        rows = parse_table(lines)
+        assert rows[0]["skip_csv"] is True
+        assert rows[0]["project"] == "Leave"
+
+    def test_normal_row_has_no_skip_csv(self):
+        rows = parse_table(WITH_DURATION)
+        assert all("skip_csv" not in r for r in rows)
+
+    def test_skip_csv_on_open_entry(self):
+        lines = [
+            "| Start | End | Project | Story | Note |",
+            "|-------|-----|---------|-------|------|",
+            "| 09:00 |     | ~Leave  |       |      |",
+        ]
+        rows = parse_table(lines, has_duration_col=False)
+        assert len(rows) == 1
+        assert rows[0]["skip_csv"] is True
+        assert rows[0]["project"] == "Leave"
+
+    def test_note_tilde_sets_skip_csv(self):
+        lines = [
+            "| Start | End   | Duration | Project | Story | Note     |",
+            "|-------|-------|----------|---------|-------|----------|",
+            "| 09:00 | 17:00 | 8:00     | Leave   |       | ~Day off |",
+        ]
+        rows = parse_table(lines)
+        assert rows[0]["skip_csv"] is True
+
+    def test_note_tilde_stripped_from_note(self):
+        lines = [
+            "| Start | End   | Duration | Project | Story | Note     |",
+            "|-------|-------|----------|---------|-------|----------|",
+            "| 09:00 | 17:00 | 8:00     | Leave   |       | ~Day off |",
+        ]
+        rows = parse_table(lines)
+        assert rows[0]["note"] == "Day off"
+
+    def test_note_tilde_with_space_stripped(self):
+        lines = [
+            "| Start | End   | Duration | Project | Story | Note      |",
+            "|-------|-------|----------|---------|-------|-------|",
+            "| 09:00 | 17:00 | 8:00     | Leave   |       | ~ Day off |",
+        ]
+        rows = parse_table(lines)
+        assert rows[0]["skip_csv"] is True
+        assert rows[0]["note"] == "Day off"
+
+    def test_note_tilde_without_duration_col(self):
+        lines = [
+            "| Start | End   | Project | Story | Note     |",
+            "|-------|-------|---------|-------|----------|",
+            "| 09:00 | 17:00 | Leave   |       | ~Day off |",
+        ]
+        rows = parse_table(lines, has_duration_col=False)
+        assert rows[0]["skip_csv"] is True
+        assert rows[0]["note"] == "Day off"
+
+    def test_note_tilde_does_not_affect_normal_row(self):
+        rows = parse_table(WITH_DURATION)
+        assert all("skip_csv" not in r for r in rows)
+
+
+class TestFilterSkipCsv:
+    def test_removes_skip_csv_rows(self):
+        rows = [
+            {"project": "Leave", "skip_csv": True, "duration_hours": 8.0},
+            {"project": "work", "duration_hours": 1.0},
+        ]
+        result = filter_skip_csv(rows)
+        assert len(result) == 1
+        assert result[0]["project"] == "work"
+
+    def test_keeps_all_normal_rows(self):
+        rows = [
+            {"project": "work", "duration_hours": 1.0},
+            {"project": "scrum", "duration_hours": 0.5},
+        ]
+        assert filter_skip_csv(rows) == rows
+
+    def test_empty_input(self):
+        assert filter_skip_csv([]) == []
+
+    def test_all_skip_csv_returns_empty(self):
+        rows = [{"project": "Leave", "skip_csv": True, "duration_hours": 8.0}]
+        assert filter_skip_csv(rows) == []
+
+    def test_rows_without_key_treated_as_normal(self):
+        """Rows that never had the key at all should pass through."""
+        rows = [{"project": "work", "duration_hours": 1.0}]
+        assert filter_skip_csv(rows) == rows
+
+
 class TestAggregateRows:
     def test_same_project_story_summed(self):
         rows = parse_table(WITH_DURATION)