[bug]: plane push silently creates duplicate work items instead of updating existing ones

Context for this and four related tickets: https://github.com/orgs/makeplane/discussions/8999

I have searched existing issues; no existing report covers this. Filing via API rather than the issue form, so the form fields (Environment, Browser, Variant, Version) are inlined below.

• Environment: Production
• Browser: Other (CLI tool)
• Variant: Cloud (tested against api.plane.so)
• Version: plane-compose 0.2.0 (note: plane --version self-reports 0.1.0 -- separate ticket forthcoming)

Current behavior

When I add a work item with an existing id (e.g. PLOC-7) to work/inbox.yaml and run plane push, Compose plans to create a new work item with a fresh sequence ID rather than update the existing one. The id field appears to be silently ignored. There is no warning, no error, and --dry-run confirms a duplicate would be created.

What I expect: push respects the id field and either updates the existing item, or fails loudly with a message like "item with id X already exists; updating existing items is not supported."

There is no documented workaround. Both plane import (referenced in the auto-generated inbox.yaml) and plane apply (referenced in the PyPI README) return No such command in 0.2.0 -- see #9000.

Steps to reproduce

1. pipx install plane-compose (installs 0.2.0).
2. plane auth login against an existing Plane Cloud workspace.
3. plane clone <uuid> --workspace <slug> for any project that has at least one work item.
4. Open .plane/remote/items.yaml, copy the YAML block for one existing item (call it PROJ-7) verbatim into work/inbox.yaml.
5. In work/inbox.yaml, change one property of that item (e.g. priority: medium -> priority: low). Leave the id: PROJ-7 field as-is.
6. Run plane push --work-only --dry-run.
7. Observe the output -- the item is listed under "Work Items to Create", and push would create a new sequence ID rather than update PROJ-7. Sample output from my run:

   Work Items Push Plan
   
                     1 Work Items to Create
   ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━┳━━━━━━━━━━┳━━━━━━━━┓
   ┃ Title                        ┃ Type ┃ Priority ┃ Labels ┃
   ┡━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━╇━━━━━━━━━━╇━━━━━━━━┩
   │ Customer reference call list │ task │ low      │        │
   └──────────────────────────────┴──────┴──────────┴────────┘
   
   Dry run mode - no changes applied
   

   Note that the id: PLOC-7 from inbox.yaml is absent from the plan, indicating it was ignored.

Start with the plane push --work-only --dry-run entry point and compare .plane/remote/items.yaml with work/inbox.yaml. Reproduce the plan using an existing item such as PROJ-7, then trace how the id field is handled. Done means an existing ID updates the item or produces a clear unsupported-operation error instead of silently scheduling a duplicate.