fix(lanes): keep stage detection honest across rollbacks and feature switches

Three defects let a lane's pipeline map claim progress that was not this
pass's work, all of them on the "going back" path a new request takes:

- `setStage` cleared the detection columns on a real transition but never
  pruned the `stages` records AHEAD of the new stage. A lane that ran through
  `done` and was then declared back at `plan` rendered `plan` as `current`
  while `tests`/`review`/`done` still read `done`, carrying the previous
  pass's evidence, and contradicting `progress` (computed from the declared
  index alone). A backwards declaration now drops every record it can prove
  is ahead; a key matching no node is unplaceable and left alone.
- `activateFeature` rewrote the live lane row for the incoming feature but
  carried the outgoing one's `detected_*` across. A never-seen slug starts at
  `stage='idle'`/`stages={}`, exactly the shape `inferredDisplayStage` renders
  from detection, so the new feature opened painted with the old one's
  progress — and forward-only rejected every real detection for it until the
  carried-over one aged past DETECTION_TTL_MS. Now cleared, like every other
  real transition; deliberately not archived, since detection is live-only.
- `codex-ingest` classified a rollout journal by raw `now - mtime`, which goes
  negative for a future mtime (clock stepped back, NTP correction, a restore
  that preserved timestamps) and read as "written milliseconds ago". A
  finished thread's journal could replay as live work; a file claiming to be
  from the future is now idle.

Also fixes `check-headers.sh`, which audited via `find` and so reported local
gitignored runtime state (a lane's own `.ccam/profile/hooks/*.sh`) that is not
this repo's source and can never be made compliant here. It now lists files
through git (tracked + untracked-but-not-ignored), so a file an agent just
wrote is still caught before it is staged while ignored state is not.

Tests: 1359 pass (4 new). Header audit exits 0.

server/lib/codex-ingest.js

@@ -266,7 +266,13 @@ function ingestCodexOnce({ broadcast } = {}) {
     if (!lane) continue;
 
     const firstSight = !offsets.has(file.path);
-    const active = Date.now() - file.mtime < CODEX_ACTIVE_MS;
+    // An mtime in the FUTURE (clock stepped back, NTP correction, a restore that
+    // preserved timestamps) makes the raw difference negative, which reads as
+    // "written milliseconds ago" and would let a finished thread's journal
+    // replay as live work. A file that claims to be from the future is not
+    // evidence of an agent working now, so treat it as idle.
+    const age = Date.now() - file.mtime;
+    const active = age >= 0 && age < CODEX_ACTIVE_MS;
     let from = firstSight ? Math.max(0, file.size - TAIL_BYTES) : offsets.get(file.path);
     // A stored offset past EOF means the file was truncated or a new thread took
     // the same path. Restart from a bounded tail, never from 0: reading a