Refactor help screen and tips to use domain.Actions as source of truth

[dnlopes]

Context

The command palette feature (#TBD) introduces domain.Actions as the canonical source of truth for what actions exist in the system. However, other components still read from different sources:

Component	Currently reads from
Help screen	KeyMap → KeyDefinitions
Tips	KeyDefinitions.TipFormat
Command palette	domain.Actions (new)

This creates inconsistency and potential for drift.

Proposed Change

Refactor the system so that:

1. domain.Actions is the canonical action catalog (Name, Description, RequiresSession)
2. KeyDefinitions references action names and adds shortcut-specific info (Defaults, TipFormat)
3. Help screen and tips derive their content by linking these two sources

Benefits

• Single source of truth for action metadata
• Consistent descriptions across all UI surfaces
• Easier to add new actions (define once in domain, wire up shortcuts in UI)

Files to Modify

• internal/ui/help_screen.go - Read from domain.Actions + KeyDefinitions
• internal/ui/keys_types.go - Tips should link to domain.Actions
• Potentially consolidate action-related code

Related

• Command palette design: docs/plans/2025-01-29-command-palette-design.md