fix(hooks/atlas): capture plan snapshot for .sisyphus paths

Oracle review of PR #3943 surfaced that endTaskTimer never fires for real Prometheus plans because their canonical path is .sisyphus/plans/ and the snapshot capture was nested inside the !isSisyphusPath branch intended for direct-work warning suppression. Move the snapshot/path tracking out of the warning gate so all plan-file edits are snapshotted regardless of .sisyphus prefix. Keep the warning branch isSisyphus-gated so Atlas does not yell at legitimate plan edits.

Regression test now uses a real .sisyphus/plans/ path and fails against HEAD before the fix.

src/hooks/atlas/tool-execute-after-task-timers.test.ts

@@ -230,7 +230,9 @@ describe("createToolExecuteAfterHandler task timers", () => {
   it("ends task timer when plan checkbox flips to checked via edit tool", async () => {
     // given
     const parentSessionID = "ses_parent_3"
-    const planPath = join(testDirectory, "task-timer-edit-plan.md")
+    const planDirectory = join(testDirectory, ".sisyphus", "plans")
+    mkdirSync(planDirectory, { recursive: true })
+    const planPath = join(planDirectory, "task-timer-edit-plan.md")
     writeFileSync(planPath, "# Plan\n\n## TODOs\n- [ ] 1. Implement auth flow\n", "utf-8")
     writeBoulderState(testDirectory, {
       schema_version: 2,