secret list gives each secret's own creation and last-update times (closes #142)

secret list and secret list --json gave the time of the listing as every
secret's creation and last-update time, because Secret.LoadMetadata set
both to the current time. It now reads file modification times, so
listing still needs no passphrase: the last update is when the secret's
current file was written, and the creation is when its oldest version's
value.age was written. A move to another vault gives the copied files
the times of the originals.

GetSecretObject no longer loads the times, so secret get keeps its error
for a missing current file; secret list calls LoadMetadata itself.

Judgement call: the creation time comes from value.age, not from the
oldest version's directory, whose time changes when the next add
rewrites that version's metadata.age.

Model: opus-5-5

TODO.md

@@ -18,6 +18,17 @@ https://git.eeqj.de/sneak/secret/milestone/12
 
 # Completed Steps
 
+- 2026-10-14: `secret list` gives each secret's own creation and last-update
+  times (https://git.eeqj.de/sneak/secret/issues/142). It gave the time of the
+  listing for both, which `Secret.LoadMetadata` set to the current time.
+  `LoadMetadata` now reads file modification times, so listing still needs no
+  passphrase: the last update is when the secret's `current` file was written,
+  and the creation is when its oldest version's `value.age` was written. That
+  version's directory would be wrong, because the next add rewrites the
+  version's `metadata.age` in it. `GetSecretObject`, which `secret get` also
+  uses, no longer loads the times; `secret list` loads them itself. A move to
+  another vault gives each copied `value.age` and `current` the modification
+  time of the file it was copied from, so the moved secret keeps its times.
 - 2026-10-14: `secret generate mnemonic`, `secret vault list` and
   `secret unlocker list` print their output to stdout, as `secret list` does, so
   it can be piped or captured (https://git.eeqj.de/sneak/secret/issues/138).