✨ Add `work` command: create work file with daily folder structure and toggle work session

[amy-shinsen-openclaw]

Context

The new folder-per-day structure is already implemented for default notes (create_note_file_with_folders + build_folder_path_for_now), producing paths like:

<not_path>/<year>/<month>/<week>/<day>/<YYYY-MM-DD>.default.md

The existing start-work and end-work commands still rely on the legacy annotation system (annotations embedded in markdown files). The new work command must not use annotations — it uses the journal.json event system instead (.nost/journal.json). The annotation system is kept as-is for legacy compatibility.

Architecture

Two parallel systems coexist:

System	Storage	Used by
Legacy	Annotations in .md files	start-work, end-work (unchanged)
New	Events in .nost/journal.json	work (new command)

Event names remain: START_WORK and STOP_WORK (matching existing EventName enum).

Behaviour

nost work   # alias: nost w

1. Resolve the work file path using build_folder_path_for_now, with type work:

   <not_path>/<year>/<month>/<week>/<day>/<YYYY-MM-DD>.work.md
   

2. Create the file (and folders) if they do not exist — reuse create_note_file_with_folders("work").
3. Check for an active session — read journal.json and find the last START_WORK or STOP_WORK event:
   • Last event is START_WORK → close the session: record a StopWork event via record_event.
   • Last event is STOP_WORK or no work event found → open a session: record a StartWork event via record_event.
4. Print a clear confirmation message indicating whether a session was opened or closed.

New module to add

src/events/find.rs — function find_last_work_event() -> Option<Event> that reads journal.json and returns the most recent event whose name is START_WORK or STOP_WORK.

Out of scope

• Stats refactoring (separate issue).
• The legacy start-work / end-work commands remain untouched.

Acceptance criteria

• nost work (alias nost w) creates <not_path>/…/<YYYY-MM-DD>.work.md on first call.
• Calling nost work twice in a row opens then closes the session.
• Calling nost work when a session is already open closes it.
• File and folder creation is idempotent (no error if already present).
• Session state is read from and written to journal.json, not from annotations.
• CI passes.

[gdarquie]

"Check for an active session — look up the last work annotation (reuse find_last_work_annotation):
Last annotation is StartWork (or no annotation found today) → open a session: write a StartWork annotation.
Last annotation is StopWork → close the session: write a StopWork annotation."

We are not supposed to use the annotation system with the new folder system: we'll use the events in "journal.json" in ".nost" folder. We will let the annotation system for now for making legacy not still working. So, I think, we have to build a parallel system able to check and add if necessary events in "journal.json" for work.

The event we can will still be "START_WORK" and "STOP_WORK".