fix(lanes): removing a lane deletes its record only, never the worktree

A lane's `remove` tore down what the lane pointed at: `git worktree remove
--force`, a branch delete, and a drop of the lane's own database. One
mis-click on a dashboard row cost a whole branch's unpushed code — and the
row is the only thing AgentHub actually owns. `remove` now stops the run and
the stack, clears AgentHub's own runtime bookkeeping under
`LANES_ROOT/.state/lane<slot>/`, and deletes the row. The working tree, its
branch, git's worktree records and the database stay exactly where they are,
for the user to delete by hand when they mean to.

That also fixes #28. Removal used to route through `assertDestroyable`, whose
third check demands the cwd appear in `git worktree list`; a managed lane
whose directory git no longer listed answered `ENOTWORKTREE` ("lane is not
listed as a worktree in …") and could never be dropped from the dashboard at
all. Removal no longer asks git anything, so no preflight blocker stops it,
and the unpushed-commits force-gate now applies to `reset` alone — nothing
`remove` does can discard a commit.

The UI follows: one label for both lane kinds ("Delete lane record"), copy
that says what survives, and no Force checkbox on removal.
`removeWorktree`/`removeLaneData` remain in place as guarded primitives; no
route calls them any more.

client/src/i18n/locales/en/lanes.json

@@ -2,7 +2,6 @@
   "action.clear": "clear state",
   "action.forget": "Delete lane",
   "action.purge": "delete history",
-  "action.remove": "delete lane + worktree",
   "action.reset": "reset worktree",
   "action.start": "start",
   "action.stop": "stop",
@@ -80,14 +79,14 @@
   "destructive.loading": "Loading current facts…",
   "destructive.notice.activeSessionSkipped": "One or more sessions in this lane are still active and will be kept, not purged.",
   "destructive.notice.adopted": "This lane points at a directory you own. Only the dashboard's record of it is dropped — the directory and its files are left untouched.",
-  "destructive.notice.missing": "The lane directory is already gone. Removing it drops the dashboard's record and clears Git's stale worktree entry; nothing is deleted from disk.",
-  "destructive.notice.unreadable": "The lane directory cannot be read as a Git worktree. Removal is attempted; if Git itself refuses, its worktree record is cleared directly instead. Either way, the directory itself is never touched.",
+  "destructive.notice.missing": "The lane directory is already gone. Deleting the lane drops the dashboard's record only; nothing on disk and no Git record is touched.",
+  "destructive.notice.unreadable": "The lane directory cannot be read as a Git worktree. That changes nothing here: only the dashboard's record is deleted, the directory is never touched.",
   "destructive.purge.confirm": "Purge history",
   "destructive.purge.message": "Approve the current counts before deleting stored session history.",
   "destructive.purge.title": "Purge lane history?",
-  "destructive.remove.confirm": "Remove lane",
-  "destructive.remove.message": "Approve the current counts before this action.",
-  "destructive.remove.title": "Remove lane?",
+  "destructive.remove.confirm": "Delete lane record",
+  "destructive.remove.message": "Only the dashboard's record of this lane is deleted. Its working tree, its branch and its database are left exactly as they are — delete them yourself if you want them gone.",
+  "destructive.remove.title": "Delete lane record?",
   "destructive.reset.confirm": "Reset worktree",
   "destructive.reset.message": "Approve the current counts before resetting this worktree.",
   "destructive.reset.survives": "Gitignored files such as node_modules and .env are kept; untracked files are deleted.",