feat(logger): add SDLOG_ROTATE, disentangle cleanup thresholds

The previous cleanup logic conflated two independent concerns into
SDLOG_MAX_SIZE: the maximum size of a single log file (rotation
trigger) AND the minimum free space to maintain. That was broken:
the 4095 MB default meant "keep 4 GB free", which over-cleaned on
large SD cards and was impossible to satisfy on small flash.

Disentangle the two:

- SDLOG_ROTATE (new, int %, default 90): maximum disk usage percentage.
  Cleanup guarantees at least (100 - SDLOG_ROTATE)% free even during
  writing of a new log file. Setting 0 disables space-based cleanup;
  100 allows filling the disk completely.
- SDLOG_MAX_SIZE (default lowered from 4095 to 1024): pure max file
  size. The value is added on top of the rotate-derived threshold as
  headroom for the next file write, so the rotate guarantee holds
  even mid-write.
- SDLOG_DIRS_MAX: removed. Directory count limits were confusing and
  orthogonal to the space-management goal; free-space cleanup alone
  covers the use case. Drop the param and all remaining overrides
  (rc.board_defaults, rcS, rc.replay, 1002_standard_vtol.hil).

Cleanup threshold is now:
    ((100 - SDLOG_ROTATE)% of disk) + SDLOG_MAX_SIZE

Small-flash boards can override SDLOG_MAX_SIZE to get more retained
logs within the available space. kakuteh7v2 and airbrainh743 drop
their SDLOG_DIRS_MAX overrides accordingly.

Update docs/en/dev_log/logging.md with the new semantics and a
worked example for the typical 8 GB SD case.

ROMFS/px4fmu_common/init.d-posix/rc.replay

@@ -20,7 +20,6 @@ module: replay
 ignore_others: false
 EOF
 
-param set SDLOG_DIRS_MAX 7
 param set SDLOG_PROFILE 3
 
 # apply all params before ekf starts, as some params cannot be changed after startup

ROMFS/px4fmu_common/init.d-posix/rcS

@@ -172,7 +172,6 @@ param set-default -s MC_AT_EN 1
 param set-default SDLOG_MODE 1
 # enable default, estimator replay and vision/avoidance logging profiles
 param set-default SDLOG_PROFILE 131
-param set-default SDLOG_DIRS_MAX 7
 
 param set-default TRIG_INTERFACE 3
 

ROMFS/px4fmu_common/init.d/airframes/1002_standard_vtol.hil

@@ -56,8 +56,6 @@ param set-default NAV_DLL_ACT 2
 param set-default RTL_DESCEND_ALT 10
 param set-default RTL_RETURN_ALT 30
 
-param set-default SDLOG_DIRS_MAX 7
-
 param set-default VT_F_TRANS_THR 0.75
 param set-default VT_TYPE 2