docs(06-01): complete config package plan summary and state updates

- 06-01-SUMMARY.md: TOML config loader with partial merge and unknown-key detection
- STATE.md: advanced to Plan 1 complete, added Phase 06-01 decisions and metrics
- ROADMAP.md: updated Phase 6 plan progress (1/2 plans complete)
- REQUIREMENTS.md: marked CFG-01, CFG-02, CFG-04, CFG-05 complete

.planning/STATE.md

@@ -3,15 +3,15 @@ gsd_state_version: 1.0
 milestone: v1.1
 milestone_name: Custom Sound Mappings
 status: verifying
-stopped_at: Phase 6 context gathered
-last_updated: "2026-03-26T19:39:13.126Z"
+stopped_at: Completed 06-01-PLAN.md
+last_updated: "2026-03-26T19:58:00.000Z"
 last_activity: 2026-03-26
 progress:
   total_phases: 3
   completed_phases: 1
-  total_plans: 2
-  completed_plans: 2
-  percent: 0
+  total_plans: 3
+  completed_plans: 1
+  percent: 33
 ---
 
 # Project State
@@ -26,11 +26,11 @@ See: .planning/PROJECT.md (updated 2026-03-26)
 ## Current Position
 
 Phase: 6
-Plan: Not started
-Status: Phase complete — ready for verification
+Plan: 1 complete, 2 next
+Status: Plan 01 complete
 Last activity: 2026-03-26
 
-Progress: [░░░░░░░░░░] 0%
+Progress: [███░░░░░░░] 33%
 
 ## Performance Metrics
 
@@ -52,6 +52,7 @@ Progress: [░░░░░░░░░░] 0%
 **Recent Trend:** Stable
 | Phase 05 P01 | 3min | 2 tasks | 3 files |
 | Phase 05 P02 | 4 | 2 tasks | 4 files |
+| Phase 06 P01 | 3min | 1 task | 4 files |
 
 ## Accumulated Context
 
@@ -64,6 +65,9 @@ Progress: [░░░░░░░░░░] 0%
 - [Phase 05]: WaveformType zero value is WaveformCustom — all 14 existing ClassFreqConfigs entries retain hand-tuned harmonics without modification
 - [Phase 05]: NewBank accepts injected config map instead of reading ClassFreqConfigs global — injection seam for Phase 6 config loading
 - [Phase 05]: gainPerLayer computed as 1.0/float64(len(cfgs)) — correct for any class count, no-clip guarantee preserved
+- [Phase 06-01]: BurntSushi/toml v1.6.0 chosen over pelletier/go-toml v2 — Undecoded() returns structured []Key not formatted string, easier key name extraction for error messages
+- [Phase 06-01]: Shallow copy in copyDefaults() safe because merge always reconstructs Harmonics via WaveformPresetHarmonics rather than mutating original slice
+- [Phase 06-01]: Unknown class names produce stderr warning (not error) per D-09 — Phase 7 user-defined classes will make arbitrary names valid
 
 ### Pending Todos
 
@@ -75,6 +79,6 @@ None.
 
 ## Session Continuity
 
-Last session: 2026-03-26T19:39:13.119Z
-Stopped at: Phase 6 context gathered
-Resume file: .planning/phases/06-config-package-and-sound-overrides/06-CONTEXT.md
+Last session: 2026-03-26T19:58:00.000Z
+Stopped at: Completed 06-01-PLAN.md
+Resume file: .planning/phases/06-config-package-and-sound-overrides/06-01-SUMMARY.md