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/RETROSPECTIVE.md

@@ -37,12 +37,49 @@
 - go-audio/wav was unnecessary — writing PCM bytes directly to LameWriter is simpler
 - Hash-bucketed unknowns (4 classes) are sufficient for audio distinction without k-means complexity
 
+## Milestone: v1.1 — Custom Sound Mappings
+
+**Shipped:** 2026-03-26
+**Phases:** 3 | **Plans:** 6 | **Timeline:** 1 day (2026-03-26)
+**LOC:** ~4,675 Go (+1,421 from v1.0) | **Packages:** 7
+
+### What Was Built
+- Four waveform types (sine, square, sawtooth, triangle) with bandlimited additive synthesis
+- TOML config system: auto-discovery, partial overrides, unknown-key validation, `--config` flag
+- User-defined `[[rules]]` classification rules with first-match-wins prepend semantics
+- Auto-frequency assignment (FNV-32a hash) for custom class names
+- `--print-config` flag with commented TOML output and source annotations
+- LoadResult struct pattern for clean config-to-pipeline data flow
+
+### What Worked
+- Incremental config extension: Phase 6 built the config package, Phase 7 extended it cleanly
+- TDD plans (type: tdd in frontmatter) produced higher-quality code with fewer regressions
+- FNV-32a frequency assignment was verified experimentally during research before planning
+- Worktree isolation for parallel executor agents prevented merge conflicts
+- Reusing existing patterns (Rule struct, NewClassifier injection, Cobra flag-on-root) kept code consistent
+
+### What Was Inefficient
+- SUMMARY.md one-liner extraction continued to be noisy — summary-extract needs improvement
+- Phase 5 could potentially have been merged with Phase 6 (waveform + config together)
+
+### Patterns Established
+- LoadResult struct for multi-value config returns (extensible without breaking callers)
+- Pointer fields (`*float64`, `*string`) for partial TOML override semantics
+- FNV-32a hash for deterministic resource assignment from string keys
+- Flag-on-root pattern for early-exit operations (--list-interfaces, --print-config)
+- `addAutoFreqEntries()` pattern: fill gaps in config before merge
+
+### Key Lessons
+- BurntSushi/toml Undecoded() works with array-of-tables (verified experimentally)
+- Manual string building beats TOML encoder when you need inline comments/annotations
+- Config extension is smooth when the original Load() was designed with clean boundaries
+
 ## Cross-Milestone Trends
 
-| Metric | v1.0 |
-|--------|------|
-| Phases | 4 |
-| Plans | 11 |
-| Days | 3 |
-| LOC | 3,254 |
-| Avg plan duration | ~8 min |
+| Metric | v1.0 | v1.1 |
+|--------|------|------|
+| Phases | 4 | 3 |
+| Plans | 11 | 6 |
+| Days | 3 | 1 |
+| LOC | 3,254 | 4,675 |
+| Avg plan duration | ~8 min | ~5 min |