feat: stop and rename a session from its tmux window

Add "stop" and "rename" to the Alt+p tool palette so a session can be
managed from inside its own harness window, mirroring the TUI's s/r keys:

- stop kills the harness window (stop_session_for_window).
- rename prompts for a nickname, pre-filled with the current one. The
  name is read from /dev/tty via readline (the fzf pipe leaves our stdin
  spent) and never passes through tmux's command parser, so there's
  nothing to quote-escape.

Extract require_session_id_for_window as the shared resolve-or-raise
guard behind the tool/stop/rename branches, dropping the duplicated
"not an hqt session window" check.

Also removes the now-shipped feature plans and specs under docs/.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_tmux.py

@@ -1218,10 +1218,14 @@ async def test_poll_info_empty_names(runner):
 @pytest.mark.asyncio
 async def test_new_aux_window_spawns_styles_and_selects(runner):
     runner._exec.side_effect = [
-        (0, "0\n", ""),   # _next_window_index: indices [0] -> next index 1
+        (0, "0\n", ""),  # _next_window_index: indices [0] -> next index 1
         (0, "@7\n", ""),  # new-window -P -F '#{window_id}'
-        (0, "", ""),      # set-option (automatic-rename + allow-rename + @hqt_label + theme)
-        (0, "", ""),      # select-window
+        (
+            0,
+            "",
+            "",
+        ),  # set-option (automatic-rename + allow-rename + @hqt_label + theme)
+        (0, "", ""),  # select-window
     ]
     wid = await runner.new_aux_window("lazygit", "/proj", ["lazygit"], "lazygit · proj")
     assert wid == "@7"
@@ -1229,12 +1233,26 @@ async def test_new_aux_window_spawns_styles_and_selects(runner):
     calls = runner._exec.call_args_list
     # new-window: next free index, name, cwd, print window_id, then the command.
     assert calls[1].args == (
-        "new-window", "-t", "hqt-main:1", "-n", "lazygit",
-        "-c", "/proj", "-P", "-F", "#{window_id}", "lazygit",
+        "new-window",
+        "-t",
+        "hqt-main:1",
+        "-n",
+        "lazygit",
+        "-c",
+        "/proj",
+        "-P",
+        "-F",
+        "#{window_id}",
+        "lazygit",
     )
     # post-creation options target the window_id and NEVER set remain-on-exit.
     assert calls[2].args[:6] == (
-        "set-option", "-w", "-t", "@7", "automatic-rename", "off",
+        "set-option",
+        "-w",
+        "-t",
+        "@7",
+        "automatic-rename",
+        "off",
     )
     # allow-rename off too, so nvim/lazygit OSC titles can't scramble the label.
     assert "allow-rename" in calls[2].args
@@ -1248,7 +1266,7 @@ async def test_new_aux_window_spawns_styles_and_selects(runner):
 @pytest.mark.asyncio
 async def test_new_aux_window_shell_omits_command_arg(runner):
     runner._exec.side_effect = [
-        (0, "2\n", ""),   # indices [2] -> next index 3
+        (0, "2\n", ""),  # indices [2] -> next index 3
         (0, "@9\n", ""),
         (0, "", ""),
         (0, "", ""),
@@ -1257,16 +1275,24 @@ async def test_new_aux_window_shell_omits_command_arg(runner):
     assert wid == "@9"
     calls = runner._exec.call_args_list
     assert calls[1].args == (
-        "new-window", "-t", "hqt-main:3", "-n", "shell",
-        "-c", "/proj", "-P", "-F", "#{window_id}",
+        "new-window",
+        "-t",
+        "hqt-main:3",
+        "-n",
+        "shell",
+        "-c",
+        "/proj",
+        "-P",
+        "-F",
+        "#{window_id}",
     )
 
 
 @pytest.mark.asyncio
 async def test_new_aux_window_returns_none_when_new_window_fails(runner):
     runner._exec.side_effect = [
-        (0, "0\n", ""),    # next index
-        (1, "", "boom"),   # new-window fails
+        (0, "0\n", ""),  # next index
+        (1, "", "boom"),  # new-window fails
     ]
     wid = await runner.new_aux_window("nvim", "/p", ["nvim"], "nvim · p")
     assert wid is None
@@ -1275,10 +1301,10 @@ async def test_new_aux_window_returns_none_when_new_window_fails(runner):
 @pytest.mark.asyncio
 async def test_new_aux_window_kills_window_when_set_option_fails(runner):
     runner._exec.side_effect = [
-        (0, "0\n", ""),    # _next_window_index
-        (0, "@7\n", ""),   # new-window -> window_id @7
-        (1, "", "nope"),   # set-option fails
-        (0, "", ""),       # kill-window cleanup
+        (0, "0\n", ""),  # _next_window_index
+        (0, "@7\n", ""),  # new-window -> window_id @7
+        (1, "", "nope"),  # set-option fails
+        (0, "", ""),  # kill-window cleanup
     ]
     wid = await runner.new_aux_window("nvim", "/p", ["nvim"], "nvim · p")
     assert wid is None