feat: multi-mint wallet with health tracking, WPA auto-detect, display gating

Squash merge of feature/multi-mint-support (21 commits):

Multi-mint wallet:
- Accept payments from 4 mints: minibits, coinos, 21mint, lnvoltz
- Periodic health probing (300s interval, 3 recovery threshold)
- Multi-wallet init with nucula_wallet_init_multi()
- /mints and /wallet API endpoints

WPA auto-detect:
- wifi_auth_mode config field (default WPA2, supports WPA3)
- Runtime mapping to wifi_auth_mode_t in STA config

Display gating:
- display_enabled config field (default true)
- Guards display_init/display_update per-board

Bug fixes:
- 3s delay before service start prevents lwip mem_free assertion
- Real npub in discovery (identity_get()->npub_hex)
- Health probe interval 300s (production value)
- Duplicate services_start_task call removed
- UTF-8 arrow replaced with ASCII in log message

Tests: 61+14 unit tests passing, firmware builds clean

1 files changed, 92 insertions, 0 deletions

diff --git a/docs/REBASE-SQUASH-MERGE-PLAN.md b/docs/REBASE-SQUASH-MERGE-PLAN.md
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+# Multi-Mint Support — Rebase, Backup, Squash & Merge Plan
+
+## Goal
+Rebase `feature/multi-mint-support` onto `master`, create a backup branch, squash all 20 commits into one clean commit, then merge to master.
+
+## Current State
+- **Branch**: `feature/multi-mint-support` in worktree `/home/c03rad0r/esp32-tollgate-multi-mint`
+- **Commits on branch**: 20 (since `master` at `77031f0`)
+- **Remote**: `origin` → Nostr relay `relay.ngit.dev` (currently down)
+- **Worktree**: shared repo — other sessions use other worktrees on different branches
+
+## Procedure
+
+### Phase 1: Pre-flight
+1. Verify working tree is clean (no uncommitted changes)
+2. Verify build passes
+3. Verify unit tests pass (75/75)
+
+### Phase 2: Backup
+4. Create backup branch `backup/multi-mint-support-pre-rebase` at current HEAD
+5. Create backup branch `backup/multi-mint-support-pre-squash` (same point, used after rebase)
+
+### Phase 3: Rebase
+6. `git rebase master` — rebase all 20 commits onto master
+7. Resolve any conflicts
+8. Verify build + tests still pass after rebase
+
+### Phase 4: Post-rebase Backup
+9. Create `backup/multi-mint-support-rebased` at the rebased HEAD
+10. This preserves every individual commit even after squashing
+
+### Phase 5: Squash
+11. `git reset --soft master` — soft reset to master, keeping all changes staged
+12. `git commit -m "feat: multi-mint Cashu wallet with health tracking, WPA auto-detect, CVM"` — single clean commit
+13. Verify build + tests pass after squash
+
+### Phase 6: Merge
+14. Merge to master (fast-forward since squashed branch sits on top)
+15. Verify master builds and tests pass
+
+## Checklist
+
+### Pre-flight
+- [ ] Working tree clean
+- [ ] Build passes (`idf.py build`)
+- [ ] Unit tests pass (`make test-unit`)
+
+### Backup
+- [ ] `backup/multi-mint-support-pre-rebase` created at current HEAD (`3aa372c`)
+
+### Rebase
+- [ ] `git rebase master` completed
+- [ ] Conflicts resolved (if any)
+- [ ] Build passes after rebase
+- [ ] Unit tests pass after rebase
+
+### Post-rebase Backup
+- [ ] `backup/multi-mint-support-rebased` created at rebased HEAD
+
+### Squash
+- [ ] `git reset --soft master` done
+- [ ] Single commit created with clean message
+- [ ] Build passes after squash
+- [ ] Unit tests pass after squash
+
+### Merge
+- [ ] Merged to master (fast-forward)
+- [ ] Master builds and tests pass
+- [ ] Worktree updated
+
+## Remaining Work After Merge
+1. **Push to Nostr relay** — blocked until `relay.ngit.dev` recovers
+2. **NVS keyset storage** — `ESP_ERR_NVS_NOT_ENOUGH_SPACE` errors; factory partition at `0x10000` limits NVS to 24KB. Options:
+   - Store keysets in SPIFFS instead of NVS
+   - Compress keyset data
+   - Only cache active keysets
+3. **Board A crash** — hardware-specific (~50s uptime), not software. Possible causes:
+   - Bad power supply on QinHeng UART adapter (serial `5A84017819`)
+   - Failing flash chip on that ESP32-S3 board
+   - Swap physical boards between UART adapters to isolate
+4. **Integration test WiFi stability** — `test-multi-mint-*` targets fail on early steps because WiFi disconnects during 30s probe wait. Fix: `_connect-b-if-needed` should run before each curl call
+5. **Display AXS15231B `ESP_ERR_NO_MEM`** — SPI flush fails every ~1s (307KB PSRAM framebuffer). The `display_enabled` config field allows disabling, but proper fix needs:
+   - Reduce framebuffer (partial refresh instead of full-screen)
+   - Or use SPI DMA with larger chunk sizes
+6. **Health probe recovery threshold** — 3 consecutive successes × 300s interval = 15min before a mint is marked reachable. Consider reducing `MINT_HEALTH_RECOVERY_THRESHOLD` to 1 for initial probes
+7. **Makefile WPA auto-detect** — `detect-wpa-security` + `generate-spiffs` + `flash-spiffs-{a,b,c}` targets added to `physical-router-test-automation/esp32/Makefile`. Needs separate commit/merge there
+
+## Backup Branch Names
+| Branch | Purpose | Created At |
+|--------|---------|------------|
+| `backup/multi-mint-support-pre-rebase` | Full history before rebase | Before `git rebase master` |
+| `backup/multi-mint-support-rebased` | All 20 commits after rebase | After `git rebase master` |