Release: add regression-tests README to .release package

Matches the pattern of EXAMPLES, DEMO, and UTILS release READMEs.
Lists all 25 test suites with test counts and descriptions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ironsheep

.release/src/regression-tests/README.md

@@ -0,0 +1,62 @@
+# Regression Test Suite
+
+Automated hardware-verified test suite for the P2 SD Card Driver. All 25 test suites (464 tests) execute on real Propeller 2 hardware with a physical SD card.
+
+## Running Tests
+
+From the `tools/` directory (one level above `src/`):
+
+```bash
+# Single suite
+./run_test.sh ../src/regression-tests/SD_RT_mount_tests.spin2
+
+# Full regression (all 24 default suites, stop-on-failure)
+./run_regression.sh
+
+# Including format test (WARNING: erases card!)
+./run_regression.sh --include-format
+```
+
+## Test Suites
+
+| Suite | Tests | Description |
+|-------|-------|-------------|
+| mount_tests | 29 | Card init, mount/unmount lifecycle |
+| file_ops_tests | 26 | Create, open, close, delete, rename |
+| read_write_tests | 48 | Data integrity, boundaries, large files |
+| seek_tests | 37 | Random access, cross-sector seeks |
+| directory_tests | 29 | Listing, navigation, deep nesting |
+| multihandle_tests | 21 | Concurrent file handles |
+| multicog_tests | 14 | Multi-cog concurrent access |
+| volume_tests | 31 | Volume label, free space, auto-flush, disk full |
+| dirhandle_tests | 25 | Directory handle enumeration |
+| subdir_ops_tests | 18 | Subdirectory file operations |
+| raw_sector_tests | 14 | Direct sector read/write |
+| multiblock_tests | 6 | Streamer DMA multi-block transfers |
+| register_tests | 10 | CID, CSD, SCR register access |
+| speed_tests | 15 | CMD6 high-speed mode |
+| crc_diag_tests | 14 | CRC counters and diagnostics |
+| crc_validation_tests | 6 | CRC error injection |
+| error_handling_tests | 14 | Error paths and misuse |
+| recovery_tests | 7 | Recovery after CRC errors |
+| fifo_tests | 21 | Inter-cog string FIFO |
+| cogcwd_tests | 5 | Per-cog working directory isolation |
+| stress_tests | 4 | Concurrent read/write stress |
+| timestamp_tests | 6 | Live clock timestamps |
+| async_tests | 6 | Non-blocking async I/O |
+| defrag_tests | 12 | Defragmentation, compaction, contiguous allocation |
+| format_tests | 46 | FAT32 format validation (optional, erases card) |
+
+## Prerequisites
+
+- **pnut-ts** and **pnut-term-ts** command-line tools
+- Parallax Propeller 2 connected via USB
+- FAT32-formatted SD card
+
+## Test Framework
+
+All tests use the shared `isp_rt_utilities.spin2` framework for assertions, guard zones, and pattern generation.
+
+---
+
+*Part of the [P2 SD Card Driver](../README.md) package -- Iron Sheep Productions*