docs(02-01): update state and roadmap after synth foundation plan

- Advance to Plan 2 of 3 in Phase 02
- Mark SYNTH-01, SYNTH-02 requirements complete
- Record decisions: go-lame v0.0.9, no go-audio/wav

.planning/STATE.md

@@ -2,13 +2,13 @@
 gsd_state_version: 1.0
 milestone: v1.0
 milestone_name: milestone
-status: Ready to plan
-stopped_at: Phase 2 context gathered
-last_updated: "2026-03-26T10:19:44.843Z"
+status: Ready to execute
+stopped_at: "Completed 02-01: synth config, oscillator, and layer"
+last_updated: "2026-03-26T10:59:51.259Z"
 progress:
   total_phases: 4
   completed_phases: 1
-  total_plans: 4
+  total_plans: 7
   completed_plans: 4
 ---
 
@@ -19,12 +19,12 @@ progress:
 See: .planning/PROJECT.md (updated 2026-03-24)
 
 **Core value:** Network traffic patterns are instantly recognizable as distinct sounds — a ping sounds different from HTTPS noise, which sounds different from a port scan.
-**Current focus:** Phase 01 — capture-and-classification
+**Current focus:** Phase 02 — audio-synthesis-engine
 
 ## Current Position
 
-Phase: 2
-Plan: Not started
+Phase: 02 (audio-synthesis-engine) — EXECUTING
+Plan: 2 of 3
 
 ## Performance Metrics
 
@@ -50,6 +50,7 @@ Plan: Not started
 | Phase 01 P03 | 8 | 2 tasks | 4 files |
 | Phase 01-capture-and-classification P02 | 3min | 1 tasks | 4 files |
 | Phase 01-capture-and-classification P04 | 15min | 2 tasks | 2 files |
+| Phase 02 P01 | 15min | 2 tasks | 8 files |
 
 ## Accumulated Context
 
@@ -73,6 +74,8 @@ Recent decisions affecting current work:
 - [Phase 01-capture-and-classification]: Dynamic link type detection via handle.LinkType() not hardcoded LinkTypeEthernet
 - [Phase 01-04]: Cobra RunE + signal.NotifyContext for clean shutdown: context cancellation is the single stop signal propagating through all three pipeline stages
 - [Phase 01-04]: Three-stage pipeline: capture -> classify goroutine -> aggregate via buffered channels; 1024-buffered classified channel absorbs burst processing
+- [Phase 02]: go-lame v0.0.9 used for MP3 encoding (embedded LAME C source, no system library needed)
+- [Phase 02]: go-audio/wav excluded — writing PCM bytes directly to LameWriter is simpler (per Claude's Discretion grant in CONTEXT.md)
 
 ### Pending Todos
 
@@ -86,6 +89,6 @@ None yet.
 
 ## Session Continuity
 
-Last session: 2026-03-26T10:19:44.836Z
-Stopped at: Phase 2 context gathered
-Resume file: .planning/phases/02-audio-synthesis-engine/02-CONTEXT.md
+Last session: 2026-03-26T10:59:51.252Z
+Stopped at: Completed 02-01: synth config, oscillator, and layer
+Resume file: None