fix: unique temp on JSON write + tolerant created_at render (v0.1.1)

- JsonStore._write used a fixed '<path>.tmp' name with no lock, so two concurrent
  authorizer invocations could clobber each other's temp and corrupt/lose the key
  store. use tempfile.mkstemp in the same dir (unique per write) then os.replace
  (atomic), cleaning up the temp on failure.
- list 'created_at' formatting did int(raw) unguarded; one hand-edited/legacy doc
  with a bad timestamp aborted the whole table. guard per-row, fall back to '-'.

verified by execution: 20 concurrent writers -> 0 errors, file stays valid JSON,
no leftover .tmp; upsert still dedupes/updates; bad/absent created_at -> '-'.

Signed-off-by: disqualifier <dev@disqualifier.me>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "envelope_authorizer"
-version = "0.1.0"
+version = "0.1.1"
 description = "CLI key-authorization manager for envelope_crypto"
 requires-python = ">=3.10"
 dependencies = [