fix(pm): spell the validator fixture's target from TARGET_OWNER, not as a slug

`check:declared-population-live` reds on main after PR B: the only path-shaped
literal `scripts/pm/fleet-write/validate.mjs` declares in its own body is the
fixture's `repo: 'objectstack-ai/objectstack'`, a slug that names no tracked
file, so the derivation reads the family as declaring a population that reaches
nothing. The fixture now spells the target as `${TARGET_OWNER}/objectstack`,
which the hint extractor admits nothing out of, so the family declares nothing
of its own and keeps the population it inherits from `RELAY_FILES` in ops.mjs.

No `no-path-population` marker: the family inherits four live leads through
the import channel, and `check:pm-dispatch-gates`' live self-test refuses a
family that carries the marker while naming paths.

Claude-Session: https://claude.ai/code/session_01VhatbEZCV5JJBoU579UBCG
Co-authored-by: Claude <noreply@anthropic.com>

Author: os-support-ai

scripts/pm/fleet-write/validate.mjs

@@ -339,11 +339,20 @@ const battery = (name) => {
 };
 let selfTestReachedVerdict = false;
 
-/** A payload every case starts from; each case mutates a copy. */
+/**
+ * A payload every case starts from; each case mutates a copy.
+ *
+ * The target is spelled from `TARGET_OWNER`, not as one quoted slug: the
+ * dispatch derivation reads every separator-bearing literal in this module's
+ * body as a path this gate declares, and a slug names no tracked file, so a
+ * bare `owner/name` here is a dead declaration `check:declared-population-live`
+ * refuses. This gate's real population is the relay's four files, inherited
+ * from `RELAY_FILES` in `ops.mjs` and checked on disk by the self-test below.
+ */
 export function fixturePayload(overrides = {}) {
   return {
     request_id: 'fw-20260922T090000Z-abc123',
-    repo: 'objectstack-ai/objectstack',
+    repo: `${TARGET_OWNER}/objectstack`,
     session: 'session_01ABCDEFGHJKMNPQRSTVWXYZ',
     actions: [{ op: 'comment', issue: 19701, body: 'Hello from the relay.' }],
     ...overrides,