chore: prune landed remote branches (closes #167)

Seventeen branches on origin whose work is in next, as the same patch or
through another pull request merged for the same issue, were deleted.
The classification and evidence for each is on the issue. Four branches
whose work never landed are kept for triage and listed in TODO.md: the
three issue 87 error-display branches and feature/show-private-key.

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

Model: opus-5-5

TODO.md

@@ -45,6 +45,17 @@ but the review is broader than any of them.
 
 # Completed Steps
 
+- 2026-10-07: Stale branches pruned from `origin`
+  ([#167](https://git.eeqj.de/sneak/AutistMask/issues/167)). Seventeen branches
+  were deleted: each one's work is in `next`, either as the same patch or
+  through another pull request merged for the same issue. The issue records the
+  evidence for each. Four are kept for triage: `fix/consistent-error-display`,
+  `fix/87-consistent-error-display` and `fix/87-consistent-error-display-v2`,
+  whose change never landed although
+  [#87](https://git.eeqj.de/sneak/AutistMask/issues/87) is closed, and
+  `feature/show-private-key`, whose README clipboard policy section is not in
+  `next`.
+
 - 2026-10-07: The toolbar icons in `icons/` can be redrawn in the tree
   ([#378](https://git.eeqj.de/sneak/AutistMask/issues/378)): `make icons` runs
   `script/lib/icons.js`, which draws the mark and writes each PNG with node's