docs: correct the _perf path references after the bench moved

The `_perf/` measurement bench was gitignored and had never been committed, so
23 of the 27 scripts cited by the perf documents were already lost. The 11
surviving files (4 scripts, cfg_dm1.json, 5 result JSONs, the 53 MB MJPG clip)
have been moved to D:\orisys_ws\docs\performance\perf-measurements\ and the
scripts patched to resolve their defaults next to themselves. The directory has
been removed from this repo.

These three files said the scripts were deleted, which was only half true:
they are moved, and the four surviving ones still run. Repointed:

- src/orisys/sensor.py: the FILTER_PRESETS comment now names the real location
  (comment only; FILTER_PRESETS itself is unchanged).
- docs/filters.md and examples/filters/README.md: the same correction for the
  latency/noise measurement provenance.

No behaviour change.

docs/filters.md

@@ -38,7 +38,8 @@
 | `balanced` | 0.5 | 3 | 0.0 | ≈2 帧（67 ms） | 建议起步档：EMA 干掉力级滤波够不到的光流抖动 |
 | `low_noise` | 0.3 | 3 | 10.0 | ≈3 帧（100 ms） | 底噪优先，读数再低通一道 |
 
-延迟换算 @60fps 减半；数字来自 `_perf/`（该目录为一次性测量脚本，已删除；对照表见
+延迟换算 @60fps 减半；数字来自 `_perf/`（该一次性目录已从 `orisys-sdk` 移除：幸存的脚本与片源
+迁到 `D:\orisys_ws\docs\performance\perf-measurements\`，其余已永久丢失；对照表见
 `D:\orisys_ws\docs\performance\orisys-sdk-perf-plan.md`，其中仍保留全部实测数字）。
 ≥1 帧的延迟与相位差是**因果滤波的代价**：旧显示端曾用零相位 `filtfilt`，那需要"未来"，
 无法在采集里做，也让"显示 == 记录"不可能——所以现在只有一条因果链。

examples/filters/README.md

@@ -7,8 +7,8 @@
 配置里**没写**的滤波键等于"关"：整段删掉就是什么都不滤，和 `off` 那段等价。
 
 背景、代价与可追溯性约定见 `docs/filters.md`；延迟/噪声实测见
-`D:\orisys_ws\docs\performance\orisys-sdk-perf-plan.md`（原 `_perf/` 测量脚本已删除，
+`D:\orisys_ws\docs\performance\orisys-sdk-perf-plan.md`（原 `_perf/` 已从本仓库移除：幸存脚本与
-该文档保留全部实测数字）。
+片源在 `D:\orisys_ws\docs\performance\perf-measurements\`，该文档保留全部实测数字）。
 
 下面每一段都有一个同目录的机器可读副本 `filters_<预设名>.json`（四个文件），
 `tests/test_filter_presets.py` 会核对它们与 `FILTER_PRESETS` 完全一致 —— 所以改预设时

src/orisys/sensor.py

@@ -57,7 +57,8 @@ DEFAULT_FLOW_EMA_ALPHA = 1.0
 #: write ``"filters": {"preset": "balanced"}`` and override any single key on
 #: top of it; the resolved values are what ``Sensor.filters_state()`` reports.
 #: The latency/noise trade-offs behind these numbers are measured in
-#: ``_perf/`` and tabulated in ``docs/filters.md``.
+#: ``docs/performance/perf-measurements/`` (moved out of the once-gitignored
+#: ``orisys-sdk/_perf/`` on 2026-09-27) and tabulated in ``docs/filters.md``.
 FILTER_PRESETS = {
     # Everything off: the file says what runs, and the raw reading is the record.
     "off": {