Add ProjectLabel support with --type flag to labels list

[iamfj]

Summary

Add support for listing ProjectLabels alongside existing IssueLabels by introducing a --type issue|project flag to labels list.

Part of #9

Background

Linear has two separate label systems:

	IssueLabel	ProjectLabel
Has team field	✅ team?: Maybe<Team>	❌ No team field
Scope	Workspace (team=null) OR team-scoped	Workspace only
Filter has team	✅ IssueLabelFilter.team	❌ Not available
Hierarchy	✅ parent, children, isGroup	✅ parent, children, isGroup

Currently only IssueLabels are supported. ProjectLabels (used for categorizing projects) are not accessible.

Design Decisions

• --type accepts issue (default) or project — no all option to avoid merged-pagination complexity. Agents can make two calls.
• --type project combined with --team produces a validation error (project labels have no team concept).
• Output adds a type field to all label results. This is a breaking change to the output shape.

Changes

GraphQL layer (graphql/queries/labels.graphql)

• Add ProjectLabelFields fragment on ProjectLabel (id, name, color, description)
• Add GetProjectLabels query on projectLabels root field with $first, $after, $filter variables
• Run npm run generate

Service layer (src/services/label-service.ts)

• Add type: "issue" | "project" to the Label interface
• Add listProjectLabels(client, options) — same pattern as listLabels but without teamId parameter, queries GetProjectLabelsDocument
• Update listLabels() to include type: "issue" in mapped output

Command layer (src/commands/labels.ts)

• Add --type <type> option with choices issue (default), project
• Route to listLabels() or listProjectLabels() based on --type
• Validate: error if --type project combined with --team

Resolver layer

No changes needed for this ticket (read-only).

Tests

• label-service.test.ts: happy path for listProjectLabels, update existing test to verify type: "issue" in output
• Validation test: --type project --team X produces error

Output Change

Before:

{ "id": "abc", "name": "Bug", "color": "#FF0000" }

After:

{ "id": "abc", "name": "Bug", "color": "#FF0000", "type": "issue" }