fix(RegionMap): compact storage /regions3, fix save/load return values, add paged region CLI output

[jirogit]

Fixes #1880 – region name memory space max out

Problem

On nRF52840 (T1000-e), the /regions2 binary format used 128 bytes of padding per record:

2 (id) + 2 (parent) + 31 (name) + 1 (flags) + 128 (pad) = 164 bytes/record
32 entries = 5,258 bytes total

This exceeds the available space in nRF52 InternalFS when shared with preferences and identity data. save() would fail silently (hardcoded return true), and on next boot load() would read a truncated file, losing region names beyond ~11 entries.

Additionally, the region CLI command was silently truncated to ~5 entries due to the single-packet reply buffer limit (~161 bytes), making it impossible to verify how many regions were actually stored.

Changes

src/helpers/RegionMap.cpp

• New /regions3 format: 64-byte padding per record (100 bytes/record, 3,210 bytes for 32 entries = 78% of one 4096B LittleFS block)
• load() prefers /regions3; falls back to /regions2 (128-byte pad) for automatic migration on next save()
• After successful save() to /regions3, deletes /regions2 if it exists
• Fixed save(): hardcoded return true → return success
• Fixed load(): hardcoded return true → return num_regions > 0 || success

examples/simple_repeater/MyMesh.cpp

• region command now supports paged output:
  • region — first page (wildcard * + entries from index 0)
  • region N — entries from index N onward
  • Footer >N at end of each page indicates the next start index
  • No footer = last page; -none- = no entries at all
• Fixes silent truncation that limited display to ~5 entries regardless of how many were stored
• Note: the mobile app UI still shows only ~5 regions due to a separate app-side limitation; that is outside the scope of this fix

Storage size comparison

Format	bytes/record	32 entries total	nRF52 4096B block usage
/regions2 (old)	164	5,258 B	1.28× ← over limit
/regions3 (new)	100	3,210 B	0.78×

Testing

Tested on Seeedstudio T1000-e:

• ✅ 32 entries with 29-character names saved and reloaded after reboot
• ✅ region save returns OK
• ✅ region / region 4 / region 8 ... paging works correctly with >N footer
• ✅ Last page shows no footer
• ⚠️ Migration from /regions2 → /regions3 not tested on physical hardware (code path verified by review only)

Fixes #2166