feat(worktree): apply the layout when opening an existing worktree

[nilp0inter]

Problem

Opening an existing worktree (via the worktree-open action) leaves Herdr's default single-shell workspace, while creating a worktree bootstraps the configured tab layout. The two paths are inconsistent: opening a previously checked-out worktree gives a bare shell instead of the user's layout.

Solution

Add an opt-in [worktree].layout_on_open config. When enabled, the three "open existing worktree" paths in the worktree flow run the same createProjectLayout bootstrap that creation uses (resolving the checkout cwd, honoring repo-local .sessionizer/config.toml overrides, then focusing):

• the open-worktree intent (an existing checkout picked from the candidate picker)
• the first worktrees.open attempt in openOrCreateWorktree (the branch already has a worktree)
• the resolver fallback that opens an existing checkout after create fails

The open-workspace intent (focusing a workspace that already exists) is intentionally left untouched — it may carry user state.

The shared logic lives in a new bootstrapOpenedWorktree helper; bootstrapWorktree gains a verb so the success log reads "opened and focused" vs "created and focused".

Default

Follows the git_only precedent from 0.5.1:

• existing configs: layout_on_open omitted → false (current focus-only behavior, non-breaking)
• newly generated configs: [worktree] layout_on_open = true

Happy to flip the missing-field default to true if you'd prefer open and create to be consistent out of the box — the gate makes either trivial.

Tests

• config: layout_on_open defaults to false in existing configs, true in generated configs, and parses from [worktree]
• worktree flow: layout applied when opening an existing worktree with the gate on (picker path, asserting exact createLayout args; and CLI --project --branch path)

bun run typecheck and bun test (140 passing) are green.

Docs

CHANGELOG (Unreleased), README config field reference + layout-source table, and the sessionizer-layout-editor skill bootstrap note/scope.

[andrewchng]

Thanks — the three open-checkout paths and leaving open-workspace as focus-only look right.

Direction change: drop [worktree].layout_on_open. Layout should always run for checkout-only open (same as create). Live workspace reattach stays focus-only, no config.

• Remove the flag from config, default TOML, README, and skill docs.
• Always bootstrap layout on the open-checkout paths; keep tests that open-workspace never calls createLayout.
• Upgrade is a mild behavior fix (open matches create), not a real break.

Conflicts: PR currently conflicts with main — please rebase/resolve (especially CHANGELOG.md) before re-review.

Changelog: yes, keep an Unreleased entry; reword after dropping the flag, e.g. “Opening an existing worktree checkout now applies the tab layout (same as create). Focusing an existing Herdr workspace is unchanged.”

Happy to re-review after that.