Adversary creator: Review step and full stat card preview

[gwillish]

Final step of the adversary creator. Displays a full preview of the new adversary as it will appear in the Compendium, with a summary of any out-of-range stats.

Scope

• Full stat card preview matching the Compendium adversary card appearance
• Out-of-range stat summary (advisory, not blocking)
• "Save" button: adds adversary to the homebrew source in Compendium with source = "homebrew"
• "Back" returns to Attacks + Features step for edits
• Saved adversary immediately available in Compendium browser

Depends on

• Stats step (Adversary creator: Stats step with inline balance range bars #42)
• Attacks + Features step (Adversary creator: Attacks and Features step #43)

Acceptance criteria

• Preview matches actual Compendium card appearance
• Out-of-range summary listed (if any) — not blocking
• Saving adds adversary to homebrew source
• New adversary appears in Compendium immediately after save
• Saved adversary can be added to an encounter builder