feat(FN-4606): complete Step 7 — docs and worktreesDir picker

Ref: Runfusion/Fusion#321
Fusion-Task-Id: FN-4606
Fusion-Task-Lineage: 94b23f37-944e-4bcd-bfa1-67d0a8c0a267

docs/settings-reference.md

@@ -228,6 +228,7 @@ Override precedence for direct merges is:
 | `recycleWorktrees` | `boolean` | `false` | Reuse worktrees from a pool for faster startup. |
 | `executorAllowSiblingBranchRename` | `boolean` | `false` | Opt back into the legacy executor behavior that silently allocates sibling branches (`fusion/<task-id>-2`, `-2-2`, …) when the canonical task branch is already checked out elsewhere. When disabled (default), branch conflicts fail loudly, leave the task in `todo` with `status: "failed"`, and expose stranded commits for explicit recovery via [`fn task branch-recovery`](./cli-reference.md#fn-task). See [Task Management → Branch conflict recovery](./task-management.md#branch-conflict-recovery). The dashboard Settings modal exposes the same toggle with warning copy because this legacy mode is discouraged. |
 | `worktreeNaming` | `"random" \| "task-id" \| "task-title"` | `"random"` | Naming mode for new worktree directories. |
+| `worktreesDir` | `string` | `undefined` | Optional container directory for task worktrees. Supports absolute paths, project-relative paths, `~` expansion, and `{repo}` token substitution (project root basename). Defaults to `<projectRoot>/.worktrees` when unset and applies to newly-created worktrees/pool scans. |
 | `taskPrefix` | `string` | `"FN"` | Prefix used for newly generated task IDs. |
 | `includeTaskIdInCommit` | `boolean` | `true` | Include task ID as commit scope in generated commits. |
 | `commitAuthorEnabled` | `boolean` | `true` | Apply explicit `--author` attribution on Fusion commits. |