set-openspec-pathlisted

Update `openspecPath` in `.claude/project-context.json` so the SessionStart hook injects the chosen project's `openspec` docs folder. This replaces hand-editing the absolute path with a menu choice. Steps: 1. Read `.claude/project-context.json` from the current project root. - If the file does not exist, tell the user to run `setup-project-context` first and stop. - If it cannot be parsed as JSON, show the parse error and stop. 2. Collect the `projects` array (entries with a non-empty `path`). Present the choices to the user with `AskUserQuestion`: - One option per registered project, labelled by `name` (falling back to `path`), with the resulting `<path>/openspec` shown in the description. - Plus a **"Clear (use working-dir openspec)"** option that sets `openspecPath` to `""` — the hook then falls back to `<project-root>/openspec` automatically. - If `projects` is empty, tell the user there are no registered projects to pick from and stop. 3. Write the result back into `.claude/project-context.json`: - For a project choice, set `openspecPath` to `<chosen project path>/openspec` (forward slashes, no trailing slash). - For "Clear", set `openspecPath` to `""`. - Preserve every other field (`roleBasedDelegation`, `projects`, ordering, formatting) unchanged — only the `openspecPath` value is modified. 4. Report the new `openspecPath` value and remind the user: - The change takes effect on the **next session sta