feat(issue-list): add -i/--include-labels flag and fix --labels parser hole

[ruby-automation]

Summary

• Add -i/--include-labels boolean flag to issue list that controls label display independently of the -l/--labels NAME filter
• Fix a silent parser hole where --labels --all consumed --all as a label name instead of erroring; now exits non-zero with a clear usage message before any API request
• Decouple label-field GraphQL selection from label-filter logic throughout the stack (cli.ex → commands.ex → issue.ex)

Changes

• app/lib/linear_cli/cli.ex: add include_labels flag (-i/--include-labels); harden parse_labels/1 to reject --prefixed tokens
• app/lib/linear_cli/cli/commands.ex: derive include_labels = flag || label_filter != []; pass to both domain input and Display.show/2
• app/lib/linear_cli/linear/issue.ex: add include_labels: :boolean argument to :list action; use args.include_labels || args.labels != [] for GraphQL document selection
• documents/ash-domain-erd.adoc: document new argument and its semantics

Test plan

• --include-labels / -i short flag requests label fields and shows them in compact output
• -N --include-labels --all sends no assignee/date filter, no label filter, requests label fields
• --labels --all exits non-zero with a clear usage error and sends no API request
• -s/--status composes with --include-labels
• Positional issue identifier with --include-labels uses full lookup and renders labels
• --output json --include-labels includes fetched label objects in stdout
• Domain-level include_labels: true with no label filter selects label fields without adding a label filter
• include_labels: false with no label filter does NOT include label fields in the query
• All 482 tests pass (format + credo strict + full test suite)

Closes EXT-45

🤖 Generated with Claude Code

[ruby-automation]

Rework: replaced non-idiomatic case with pattern-matched function heads

Per review feedback on the parse_labels implementation at cli.ex:491:

Replaced the case Enum.find(...) block dispatching on nil vs. a value with two parse_labels_result/2 function clauses — one matching nil (valid input), one matching any other term (bad token). The logic is unchanged; only the form is idiomatic.

Quality gate: 482 tests pass, credo --strict clean, format clean.