Code-review fixes for #60: USB MSC hardening + low-severity cleanups

[TheAngryRaven]

Multi-agent code review of #60 surfaced two CRITICAL structural defects in the newly-added USB Mass Storage feature plus a handful of lower-severity issues. This branch fixes them, one commit per fix for auditability. All 121 host tests pass and the test build is clean.

Fixes (severity order)

Severity	Fix
🔴 CRITICAL	Park the main loop while USB MSC is active. While the drive was mounted, loop() kept running GPS_LOOP(), trackDetectionLoop(), checkAutoIdle(), etc., so the firmware and the host PC could both drive the FAT — corruption was prevented only as a side effect of the SD-access mutex denying those acquires, not by design. loop() now early-returns on usbMscActive (mirroring the bleActive branch), servicing only the Exit button and the status page.
🔴 CRITICAL	Exit USB mode when the cable is unplugged. The only exit was the on-device Exit button; pulling the cable left the device stuck usbMscActive, holding SD_ACCESS_USB_MSC and the EMI-unsafe 8 MHz SD clock forever — a subsequent drive would then be silently denied logging. The parked branch now watches VBUS and reboots out of USB mode on disconnect.
🟠 HIGH	Check usb_msc.begin() result + lengthen re-enumeration delay. begin()'s bool was ignored, so a failed MSC registration still flipped usbMscActive and re-enumerated, stranding the user on a "drive active" screen with no drive. Now bails cleanly (restore clock, release lock, return false). Detach delay raised 10 ms → 50 ms (10 ms is below the USB spec's recommended settle window).
🟡 MEDIUM	Validate sector alignment + retry in the MSC read/write callbacks. A non-multiple bufsize silently dropped a partial sector via integer division. Now reject zero/unaligned sizes and retry the SD op up to 3× (matching the EMI-hardening retry pattern used elsewhere).
🟡 MEDIUM	Flush card + drop media-ready before the exit reboot. USB_MSC_DISABLE() went straight to reset, relying on the host having ejected first; an un-ejected exit could lose a buffered write / leave the FAT inconsistent. Now setUnitReady(false) + syncDevice() before resetting.
🟡 MEDIUM	Reject over-length BLE filename commands. The file-request callback truncated commands to 64 bytes and then validated/path-built the mangled name. Raw-data paths (track upload, OTA chunks) already return earlier, so a len >= 65 command at dispatch is malformed — now rejected with ERROR.
🟢 LOW	Pin kSpace minutes>0 seconds zero-padding with a column-stability test + CHANGELOG note (cosmetic 1: 5.007 → 1:05.007 change from the lap_format refactor).

CHANGELOG.md and CLAUDE.md updated alongside the behavior changes.

Lows deliberately left as-is

• forceReleaseSDAccess() policy bypass — dead code (zero callers); left the exported API untouched.
• Tach overflow transient-discard — an accuracy coast (Kalman + 2 s sanity bound absorb it), not corruption; the suggested tightening touches the timing-critical ISR SPSC logic and isn't worth the risk.
• bleSendFileList lock-hold / TRACK_PARSE-preemptible invariant — accepted by review (recovered by the 1 Hz log-open retry / correct under current synchronous usage).
• USB revision string "1.0" — can't use FIRMWARE_VERSION ("2.2.3" is 5 chars; the MSC revision field caps at 4), so the current value is correct.

🤖 Generated with Claude Code

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Coverage — host-testable units

📂 Overall coverage

Metric	Coverage
Lines	🟢 259/260 (99.6%)
Functions	🟢 26/26 (100.0%)
Branches	🟡 237/271 (87.5%)

📄 File coverage

File	Lines	Functions	Branches
BirdsEye/crc32.cpp	🟢 30/30 (100.0%)	🟢 4/4 (100.0%)	🟢 24/24 (100.0%)
BirdsEye/dovex_header.cpp	🟢 100/101 (99.0%)	🟢 6/6 (100.0%)	🔴 61/92 (66.3%)
BirdsEye/filename_validator.cpp	🟢 14/14 (100.0%)	🟢 1/1 (100.0%)	🟢 30/30 (100.0%)
BirdsEye/gps_time.cpp	🟢 45/45 (100.0%)	🟢 6/6 (100.0%)	🟢 30/32 (93.8%)
BirdsEye/gps_validation.cpp	🟢 24/24 (100.0%)	🟢 2/2 (100.0%)	🟢 66/66 (100.0%)
BirdsEye/haversine.cpp	🟢 8/8 (100.0%)	🟢 1/1 (100.0%)	⚫ 0/0 (0.0%)
BirdsEye/lap_format.cpp	🟢 18/18 (100.0%)	🟢 1/1 (100.0%)	🟢 9/9 (100.0%)
BirdsEye/sd_access_policy.cpp	🟢 5/5 (100.0%)	🟢 2/2 (100.0%)	🟢 10/10 (100.0%)
BirdsEye/tach_filter.cpp	🟢 15/15 (100.0%)	🟢 3/3 (100.0%)	🟡 7/8 (87.5%)