chore: prune landed remote branches (closes #167)

Seventeen branches on origin that the issue classifies as landed, or
superseded by a merged pull request, were deleted; the evidence for each
is on the issue. Five whose work is not in next are kept: the three
issue 87 error-display branches and feature/show-private-key, reference
for issues 493 and 492, and chore/token-list-enrichment, re-created at
f7a2437, pending issue 495. TODO.md records this.

The branch-pruning Future Step had already left TODO.md in the issue 191
rewrite, so only the Completed Steps entry is added.

Model: opus-5-5

TODO.md

@@ -47,18 +47,23 @@ but the review is broader than any of them.
 
 - 2026-10-07: Stale branches pruned from `origin`
   ([#167](https://git.eeqj.de/sneak/AutistMask/issues/167)). The issue
-  classifies each branch it lists, with the evidence. The eighteen still on
+  classifies each branch it lists, with the evidence. The seventeen still on
-  `origin` that it classifies as landed, or superseded by merged pull requests,
+  `origin` that it classifies as landed, or superseded by a merged pull request,
   were deleted. `feat/message-signing` and `fix/59-transaction-view-ui-policies`
-  had been deleted on 2026-09-09; both landed and stay deleted. Four are kept
+  had been deleted on 2026-09-09; both landed and stay deleted. Five are kept
   because their work is not in `next`: `fix/consistent-error-display`,
   `fix/87-consistent-error-display` and `fix/87-consistent-error-display-v2`,
   the change for [#87](https://git.eeqj.de/sneak/AutistMask/issues/87) that
   never landed, as reference for
-  [#493](https://git.eeqj.de/sneak/AutistMask/issues/493); and
+  [#493](https://git.eeqj.de/sneak/AutistMask/issues/493);
+  `feature/show-private-key`, whose README clipboard policy section was the
+  reference for [#492](https://git.eeqj.de/sneak/AutistMask/issues/492); and
   `chore/token-list-enrichment`, deleted on 2026-09-09 and re-created at
   `f7a2437`, whose `scripts/` tooling waits on
-  [#495](https://git.eeqj.de/sneak/AutistMask/issues/495).
+  [#495](https://git.eeqj.de/sneak/AutistMask/issues/495). Afterwards
+  `git ls-remote --heads origin` showed `main`, `next`, these five, and
+  `issue-167-prune-branches`, the head of
+  [#491](https://git.eeqj.de/sneak/AutistMask/pulls/491).
 
 - 2026-10-07: The README says that the wallet never clears the clipboard after
   the private key or the recovery phrase is copied, and why