chore: archive v1.0 MVP milestone

Archive roadmap and requirements to milestones/, reorganize ROADMAP.md,
evolve PROJECT.md with shipped state, create retrospective.

4 phases, 11 plans, 16/16 requirements — all complete.

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

.planning/RETROSPECTIVE.md

@@ -0,0 +1,48 @@
+# Retrospective
+
+## Milestone: v1.0 — MVP
+
+**Shipped:** 2026-03-26
+**Phases:** 4 | **Plans:** 11 | **Timeline:** 3 days (2026-03-24 -> 2026-03-26)
+**LOC:** 3,254 Go | **Files:** 84 modified
+
+### What Was Built
+- Config-driven packet classifier with 12 protocol rules and 4 hash-bucketed unknown classes
+- Live packet capture via pure Go go-pcap with privilege detection and non-blocking channel pipeline
+- Additive synthesis engine: per-class oscillators, EMA amplitude smoothing, constant-power stereo mixing
+- MP3 encoding via embedded LAME, zero-packet guard
+- End-to-end pipeline with clean Ctrl+C shutdown
+- BPF filter and offline pcap file sonification with timestamp-based windowing
+
+### What Worked
+- Risk-ordered phases: hardest foundation first (capture), then synthesis in isolation, then integration — no phase blocked on another's bugs
+- TDD approach in executor agents caught signature mismatches early
+- Pure Go capture layer (go-pcap) avoided libpcap dependency headaches
+- Hand-rolled synthesis kept dependencies minimal and code understandable
+- Wave-based parallel execution for independent plans
+
+### What Was Inefficient
+- Some SUMMARY.md files had empty one-liner fields, causing noisy milestone extraction
+- Phase 4 research could have been lighter — BPF/pcap APIs were straightforward
+
+### Patterns Established
+- Ordered []Rule slice for classifier (first-match-wins, extensible)
+- io.Writer injection for testable stderr output
+- Buffered channels between pipeline stages (512-1024) to absorb bursts
+- Package-level globals for Cobra flag binding
+- Timestamp-based windowing for non-live sources
+
+### Key Lessons
+- Embedding C source (go-lame) is a good tradeoff: CGo at build time only, no runtime dependency
+- 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
+
+## Cross-Milestone Trends
+
+| Metric | v1.0 |
+|--------|------|
+| Phases | 4 |
+| Plans | 11 |
+| Days | 3 |
+| LOC | 3,254 |
+| Avg plan duration | ~8 min |