settings: add host instrument profiles (#753)

* settings: add host instrument profiles

Signed-off-by: ChrisBeWithYou <christian.a.cowan@gmail.com>

* settings: add instrument pathway selection

Signed-off-by: ChrisBeWithYou <christian.a.cowan@gmail.com>

* fix(settings): profile-aware saves/resets/switch, provider tunings, bass-5

Five regressions from the instrument-profiles rework:

1. save_settings canonicalized profiles on EVERY save -> empty/unrelated POST
   froze default profiles into config.json (broke
   test_empty_post_preserves_all_existing_keys). Gate on the save touching
   instrument settings; GET already virtualizes profiles.
2. pathway is profile-mirrored, so the Gameplay reset (flat-key delete) was a
   no-op. reset_settings now resets pathway inside the persisted profiles too.
3. Per-profile tuning validation rejected provider/custom tunings (tuner
   plugin, /api/tunings). _valid_tuning_for_key now accepts a name unknown to
   every built-in table while still rejecting a built-in misapplied to the
   wrong key.
4. First-migration overwrote an explicit active_instrument_profile with the
   legacy-inferred one, so a fresh-config switch to 'bass' was lost. Use
   setdefault so an explicit request wins.
5. Pre-existing test_instrument_fields_persist used bass-5 + 'Drop D' (a
   4-string tuning). Updated to the valid 'Drop A'.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(settings): partial-merge instrument_profiles; clamp tuning on string-count switch

Two partial-update follow-ups:
- save_settings normalized a POSTed instrument_profiles by FILLING every omitted
  profile with defaults and replacing wholesale, so a one-profile update reset
  the others. Validate each PROVIDED profile individually and merge the partial
  over the persisted set inside the lock — /api/settings is partial-merge.
- the string-count picker posted only string_count, so the backend silently
  reset a now-invalid tuning to Standard while the UI kept the old value
  (settings/tuner desync). Clamp + post the valid tuning too, mirroring the
  instrument-switch path.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Signed-off-by: ChrisBeWithYou <christian.a.cowan@gmail.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

static/app.js

@@ -2758,6 +2758,12 @@ function goFavTreePage(p) {
 // ── Settings ─────────────────────────────────────────────────────────────
 let _defaultArrangement = '';
 
+const INSTRUMENT_PATHWAYS = ['songs', 'practice', 'learn', 'studio'];
+
+function _normalizeInstrumentPathway(value) {
+    return INSTRUMENT_PATHWAYS.includes(value) ? value : 'songs';
+}
+
 function _syncDefaultArrangementSelect(value) {
     const sel = document.getElementById('default-arrangement');
     if (!sel) return;
@@ -3410,6 +3416,8 @@ async function loadSettings() {
     if (dlcEl) dlcEl.value = data.dlc_dir || '';
     _defaultArrangement = data.default_arrangement || '';
     _syncDefaultArrangementSelect(_defaultArrangement);
+    const pathwayEl = document.getElementById('setting-instrument-pathway');
+    if (pathwayEl) pathwayEl.value = _normalizeInstrumentPathway(data.pathway);
     const demucsEl = document.getElementById('demucs-server-url');
     if (demucsEl) demucsEl.value = data.demucs_server_url || '';
     const leftyEl = document.getElementById('setting-lefty');
@@ -3901,6 +3909,18 @@ function persistSetting(key, value) {
     _settingSaveChain = next.catch(() => {});
     return next;
 }
+function setInstrumentPathway(value) {
+    const pathway = _normalizeInstrumentPathway(value);
+    const el = document.getElementById('setting-instrument-pathway');
+    if (el) el.value = pathway;
+    persistSetting('pathway', pathway).then(() => {
+        if (window.v3Badges && typeof window.v3Badges.reload === 'function') {
+            try { window.v3Badges.reload(); } catch (_) { /* noop */ }
+        }
+    });
+}
+
+
 async function _postSetting(key, value) {
     const status = document.getElementById('settings-status');
     try {