feat(heal): incremental status cursors and typed overlap policy (HS-06) (#6206)

* feat(heal): incremental heal status cursors and typed overlap policy (HS-06)

Incremental results: every retained result item now carries a monotonic
sequence number. The status query accepts a client cursor (sinceSeq on
the admin wire, Option<u64> internally) and returns only newer items,
plus nextSeq (the next cursor) and minSeq (the oldest retained
sequence). A cursor that fell behind the 1024-item retention window is
flagged through the existing truncated signal together with minSeq so
the client can restart from it. Sequencing survives task completion:
the completion archive stores the seq-stamped window. None keeps the
exact legacy full-snapshot behavior, so existing clients see no change.

Typed overlap handling for admin starts: RUSTFS_HEAL_OVERLAP_POLICY
(merge default | minio_error). Under minio_error, an admin start whose
path overlaps an active or queued task rejects with typed
already-running / overlapping-paths admission reasons (surfaced through
reason_label in the admin error body, sharing the existing
OperationAborted site because the s3s footprint ratchet forbids new
s3_error! sites); an exact duplicate start rejects with
already-running instead of silently merging. Scanner/autoheal/
read-repair sources never take the rejection path.

forceStart semantics now match MinIO for admin requests: an admin
forceStart first cancels the overlapping active admin task, then
admits the replacement.

Wire: the heal-control Query command grows an optional sinceSeq
(defaulted and skipped when absent, so older peers stay compatible);
the admin handler accepts the sinceSeq query parameter; the local
channel query gains the same cursor.

Tests: seq monotonicity and incremental slicing, window slide moving
minSeq with lagging-cursor flags, overlap matrix (same/containing/
contained/disjoint x policy x source), forceStart cancel-then-admit,
and the completion-archive window handoff.

Co-Authored-By: heihutu <heihutu@gmail.com>

* style: fmt after main merge

---------

Co-authored-by: heihutu <heihutu@gmail.com>
Co-authored-by: zhi22915 <qiuzgang@gmail.com>

scripts/check_s3s_footprint.sh

@@ -25,7 +25,7 @@ cd "$(dirname "$0")/.."
 # Baselines verified on 2026-08-11. Lower-only; see header.
 # Excludes crates/e2e_test/ — test infrastructure legitimately uses s3s
 # to verify S3 behavior and does not widen the production s3s surface.
-S3S_IMPORT_FILES_BASELINE=213
+S3S_IMPORT_FILES_BASELINE=211
 S3_ERROR_LINES_BASELINE=1620
 S3S_PATH_PATTERN='(^|[^"[:alnum:]_])s3s::'
 E2E_TEST_GLOB='--glob=!crates/e2e_test/**'