fix(projects): auto-generate identifier on project create

[OmarAdel10]

Summary

Fixes project new <name> failing when no -i flag is given. The Plane API requires a project identifier, but the CLI previously sent CreateProject(name=...) with no identifier, causing the create to be rejected. The identifier is now auto-generated from the project name (first 5 alphanumeric characters, uppercased) when not explicitly provided.

Problem

planecli project new "My Project"

sent CreateProject with a missing identifier field. The Plane API rejects project creation without an identifier, so the command failed unless the user remembered to pass -i FE etc. The --help text already documented "Auto-generated if not specified" — this PR makes the CLI honor that contract.

Change

• src/planecli/commands/projects.py
  • New _default_identifier(name) helper: derives an identifier from the project name (alphanumeric characters only, max 5, uppercased).
  • create now always sends an identifier: the explicit -i value wins; otherwise the derived default is used. Explicit identifiers are still uppercased as before.
• tests/test_projects.py (new)
  • Covers derivation from a normal name, punctuation stripping, short names, and uppercasing.

Behavior

Before	After
project new "My Backend API" → API error (missing identifier)	project new "My Backend API" → created with identifier MYBAC
project new "API" -i fe → created with FE	unchanged (FE)

No breaking changes. No output-format changes.

Testing

make check (ruff format + ruff lint + pytest) — all green:

145 passed in 1.91s

Includes the 4 new tests/test_projects.py tests.

Notes

• Single-file source change; submitted via fork (OmarAdel10/plane-cli) since write access to this repo is not available.
• Branch: fix/project-create-auto-identifier