chore: complete v1.1 milestone — Custom Sound Mappings

Archive roadmap and requirements to milestones/, update PROJECT.md
with shipped state, collapse ROADMAP.md, update retrospective.

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

.planning/MILESTONES.md

@@ -1,5 +1,20 @@
 # Milestones
 
+## v1.1 Custom Sound Mappings (Shipped: 2026-03-26)
+
+**Phases completed:** 3 phases, 6 plans, 3 tasks
+
+**Key accomplishments:**
+
+- Four waveform types (sine, square, sawtooth, triangle) with bandlimited additive synthesis and decoupled bank injection
+- TOML config system with auto-discovery, partial override semantics, unknown-key validation, and `--config` flag
+- User-defined classification rules via `[[rules]]` TOML blocks — prepend before built-ins, first-match-wins
+- Auto-frequency assignment (FNV-32a hash, 1200-2350 Hz) for custom class names with no sound config
+- `--print-config` flag outputs full effective config as commented TOML with source annotations
+- End-to-end config flow: TOML file -> config.Load() -> LoadResult -> synthesis pipeline
+
+---
+
 ## v1.0 MVP (Shipped: 2026-03-26)
 
 **Phases completed:** 4 phases, 11 plans, 9 tasks