feat: add entire sessions stop command

[peyton-alt]

Summary

Adds entire sessions stop to manually mark one or more active sessions as ended, preventing future checkpoint leakage without waiting for the agent to stop naturally.

• Introduces entire sessions parent command to group session management
• Pure state mutation — no writes to the checkpoints branch, no condensation. The existing PostCommit hook handles any remaining condensation on the next commit.
• Session ID is a positional argument: entire sessions stop <session-id>
• Flags: --all (worktree-scoped), -f/--force (skip confirmation)
• All paths (no args, positional ID, --all) require confirmation unless --force is set

Usage

entire sessions stop                     # Interactive: confirm single / multi-select
entire sessions stop <session-id>        # Stop a specific session by ID
entire sessions stop --all               # Stop all active sessions in current worktree
entire sessions stop --force             # Skip confirmation prompt

Output

Session with a committed checkpoint:

✓ Session 2026-03-19-demo-checkpoint stopped.
  Checkpoint: a3b2c4d5e6f7

Session with uncommitted work:

✓ Session 2026-03-19-demo-uncommitted stopped.
  Work will be captured in your next checkpoint.

Session with no recorded work:

✓ Session 2026-03-19-demo-empty stopped.
  No work recorded.

Test plan

• mise run fmt && mise run lint passes
• mise run test:ci passes (unit + integration + E2E canary)
• entire sessions stop --help shows correct usage with positional arg
• Tests cover: no sessions, single session, --all, positional session ID, worktree scoping, already-stopped, not-a-git-repo, mutual exclusion of --all + session ID arg, batch stop, legacy sessions with empty WorktreePath, confirmation prompt consistency

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[Copilot]

Pull request overview

Adds a new entire stop command to manually mark one or more sessions as ended (state-only mutation) to prevent further checkpoint leakage without waiting for the agent lifecycle to naturally close the session.

Changes:

• Introduces entire stop with --session, --all (worktree-scoped), and --force flows, including interactive selection when multiple sessions exist.
• Adds unit tests covering the non-interactive stop flows and common error cases.
• Documents the new command in README.md and CHANGELOG.md, and wires it into the root command.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
README.md	Adds entire stop to the command list.
cmd/entire/cli/stop.go	Implements the stop command logic (single/all/multi-select) and output messaging.
cmd/entire/cli/stop_test.go	Adds unit tests for stop behavior (force, flags, not-found, non-git repo, etc.).
cmd/entire/cli/root.go	Registers the new stop subcommand.
CHANGELOG.md	Notes the addition of entire stop.