fix: review follow-ups for the session archive set

- WorkspaceRegistry.archiveSession no longer wraps persistence-listing
  failures as WorkspaceUnknownSessionError: only a definite miss (live
  lookup, header index, then a fresh list) maps to session-not-found;
  storage faults propagate as internal errors, with a negative test.
- The archived-current sweep moves from the unary path into the
  projection: any install path (local echo, another tab's frame, a
  reconnect baseline) clears a selection that landed in the archive set.
- An archive set installed while workspace.list is in flight supersedes
  the stale baseline's set instead of being rolled back by it.
- The workspace-management e2e anchors the archived row by its session
  actions button and asserts the single-stray fixture assumption loudly.
- Drop the stale touchSession rows from the workspace READMEs (the
  method was removed with its Agent Note).

packages/client/runtime/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/client/runtime/README.md
-README.md: 4c9122d87bfb0ea2d66478de03c69975b0577ab7
-README.zh.md: 1ee4731964ea75de29da47137933852581fc45b3
+README.md: 52d2caf51d2fdaf48a06e6d56292fe087568eba5
+README.zh.md: d7e807cd7dffdd81a106488884031fccbb8a6d65