feat: clear_table — empty the roster on a table change

"Clear the table" had no tool behind it, so she claimed she did it and nothing
changed. Add clear_table (empties the roster, keeps the session/stack/reads) and
a `replace` flag on seat_players for a one-shot table swap. Cash card: on a table
change / "clear the table", call clear_table then seat the new table — never claim
it without calling the tool.

2 tests. Full suite green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_roster.py

@@ -72,6 +72,28 @@ def test_unseat_player_removes_from_roster_keeps_history(mods):
     assert poker.player_profile("TAG")["reads"]         # history intact
 
 
+def test_clear_table_empties_roster_keeps_reads(mods):
+    poker, tools = mods
+    poker.start_session(venue="Meadows", buy_in=300)
+    poker.seat_players(["TAG", "Jonathan"])
+    poker.add_read(note="limped A4o", name="TAG")
+    out = tools.dispatch("clear_table", {}, {})
+    assert "cleared" in out.lower()
+    assert poker.session_roster() == []                     # roster emptied
+    assert poker.player_profile("TAG")["reads"]             # reads kept
+    # A live session is untouched by clearing the table.
+    assert poker.live_session() is not None
+
+
+def test_seat_players_replace_swaps_to_new_table(mods):
+    poker, tools = mods
+    poker.start_session(venue="Meadows", buy_in=300)
+    poker.seat_players(["TAG", "Jonathan"])
+    tools.dispatch("seat_players", {"players": [{"name": "Doyle"}, {"name": "Ivey"}],
+                                    "replace": True}, {})
+    assert {r["name"] for r in poker.session_roster()} == {"Doyle", "Ivey"}
+
+
 def test_seat_players_accepts_plain_name_list_via_tool(mods):
     poker, tools = mods
     poker.start_session(venue="Meadows", buy_in=300)