feat(docs): add brief and brand reference docs to phase-2 branch

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/brief/lifetime-licence-economics.md

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+<!-- Source: Kon Master Brief — §16 Lifetime Licence Economics -->
+
+## 16. Lifetime Licence Economics
+
+### Proven models
+- **Affinity (Serif):** Perpetual licences (~£40/app, £135 suite) for 23 years. 53% profit margins. Acquired by Canva for ~£410M.
+- **iA Writer:** £40 Mac, £24 Windows, £16 iOS one-time. Free updates for 7+ years. Profitable with team of 12, entirely bootstrapped. Android experiment showed 50/50 split between one-time (£24) and subscription (£4/year), but purchases generated 2–3x more total revenue with significantly better retention.
+- **Sublime Text:** £79 perpetual licence with paid major-version upgrades. Sustained a tiny team for over a decade.
+- **Obsidian:** Free core + £3.20/month Sync, £6.40/month Publish. Clearest precedent for Kon's hybrid model.
+
+### Risks
+- Revenue plateaus once addressable market is saturated, while support costs continue indefinitely.
+- Wondershare Filmora attempted to retroactively limit lifetime holders — massive backlash, forced apology. Lesson: never revoke or downgrade promised features.
+- AppSumo lifetime deals carry 40% failure rate within 3 years (but this reflects underpriced SaaS with cloud costs, not local-first desktop apps).
+- 35% of apps now mix subscriptions with lifetime purchases (RevenueCat 2026 data).