[M10/LNS-005] Wire CLI colon syntax for view:lens chaining

[flyingrobots]

LNS-005: Wire CLI Colon Syntax

Parent: #227 (M10 LENS)

What

Wire the view:lens1:lens2 colon syntax into the CLI:

• Split view argument on : in bin/git-mind.js + src/cli/commands.js:83-109
• First segment = view name, remaining segments = lens names
• Update formatView header in src/cli/format.js to show applied lenses
• Add lenses field to --json output

Why

This is the user-facing UX for lens composition. Must feel natural and match the documented syntax.

Acceptance Criteria

• git mind view roadmap:incomplete works
• git mind view roadmap:incomplete:frontier chains two lenses
• Invalid lens name → helpful error listing available lenses
• Terminal header shows roadmap:incomplete (or similar)
• --json output includes lenses array in metadata
• Help text updated for view command
• Integration tests with real graph fixtures

Dependencies

• LNS-003 (composition engine)
• LNS-004 (core lenses exist to test with)

[flyingrobots]

Implemented in M10 LENS milestone. Closing as done.