Record the defect-hunt fixes in TODO.md Completed Steps (closes #334)

Adds a Completed Steps entry, newest first, for every issue from the
defect hunt (#288) that a merged
fix closed and that had none: the hunt's own issues, those filed while
fixing them, and the owner's ruling on
#239. Each entry was checked
against the code on `next`. Next Step now says the hunt's fixes have
landed.

Judgement call: #332, closed as
covered by the fix for #296, is
named in that entry rather than given its own.
Judgement call: #351, a Docker
build fix filed while gating these fixes, gets an entry.

Model: opus-5-5

TODO.md

@@ -185,8 +185,8 @@ owner's; a `v*` tag runs the release build in
   makes an anchored pattern match at every depth too, and each `/**/`
   inside a pattern also matches a single `/`.
 
-- 2026-10-13: Made the `chunk_size` and `blob_size_limit` defaults and
+- 2026-10-13: Made the size defaults and the `chunk_size` minimum
-  the `chunk_size` minimum 1000-based
+  1000-based
   ([issue #313](https://git.eeqj.de/sneak/vaultik/issues/313)). They
   were 1024-based while the size parser, the docs and `info` use
   1000-based units, so `chunk_size: 1MB` was rejected, writing out a
@@ -259,10 +259,9 @@ owner's; a `v*` tag runs the release build in
   backup runs
   ([issue #360](https://git.eeqj.de/sneak/vaultik/issues/360)).
   `snapshot list` summed the chunks a snapshot reaches through file
-  rows shared by every snapshot that lists the file and that a changed
+  rows that every snapshot shares and that a changed file rewrites, so
-  file rewrites, so backing up a changed file changed the UNCOMPRESSED
+  backing up a changed file changed every older snapshot's UNCOMPRESSED
-  SIZE of every older snapshot that lists that file. The backup now
+  SIZE. The backup now stores that total in the `snapshots` table's
-  stores that total in the `snapshots` table's
   `uncompressed_chunk_size`, which `snapshot list` reads.
 
 - 2026-10-13: Stopped `snapshot restore --verify` reporting a file that
@@ -334,12 +333,12 @@ owner's; a `v*` tag runs the release build in
 
 - 2026-10-13: Recorded each snapshot's new chunk size when its backup
   runs ([issue #311](https://git.eeqj.de/sneak/vaultik/issues/311)).
-  `snapshot list` worked out NEW CHUNK SIZE from file rows shared by
+  `snapshot list` worked out NEW CHUNK SIZE from file rows that every
-  every snapshot that lists the file and that a changed file rewrites,
+  snapshot shares and that a changed file rewrites, so a snapshot whose
-  so a snapshot whose change was a modified file showed 0 B and older
+  change was a modified file showed 0 B and older snapshots' figures
-  snapshots' figures moved after later backups. The backup now stores
+  moved after later backups. The backup now stores the size of the
-  the size of the chunks it newly stored in the `snapshots` table's
+  chunks it newly stored in the `snapshots` table's `new_chunk_size`,
-  `new_chunk_size`, which `snapshot list` reads.
+  which `snapshot list` reads.
 
 - 2026-10-13: Made a backup interrupted during a local index write exit
   as interrupted