chore(deps): bump mppx to 0.12.0 (#159)

Bumps `mppx` from `0.8.14` to `0.12.0` ([release
notes](https://github.com/wevm/mppx/releases/tag/mppx%400.12.0)).

## Dependency changes

- `package.json`: `mppx` `0.8.14` -> `0.12.0`; `viem` `2.55.10` ->
`2.57.1` (mppx 0.12.0 requires peer `viem >=2.57.1`)
- `pnpm-workspace.yaml`: adds `minimumReleaseAgeExclude` for
`mppx@0.12.0` and `viem@2.57.1`. Both were released today and would
otherwise be blocked by the 7-day `minimumReleaseAge`
- `pnpm-lock.yaml` regenerated with `pnpm install`. `accounts@0.17.3`
still pulls its own exact-pinned `mppx@0.8.14` transitively
- `.changelog/bump-mppx-0-12-0.md`: patch changelog entry

## Code changes

None. The CLI's use of `Challenge`, `Credential`, `PaymentRequest`,
`Mppx`, `session`, `tempo` and `Session` from `mppx` / `mppx/client` /
`mppx/tempo` typechecks unchanged against 0.12.0.

## Validation

- `pnpm typecheck`, `pnpm test:types`, `pnpm build` pass
- `pnpm check:lint` passes
- `pnpm changelog:validate` passes
- `pnpm bundle` passes, and `node dist-package/tempo-wallet.cjs --help`
runs
- `pnpm test`: all pass except 8 tests in `test/identity.test.ts` and
`test/session-close-exit.test.ts`. They fail with `spawn sqlite3 ENOENT`
because the validation sandbox has no `sqlite3` binary, which is
unrelated to this change
- `pnpm check:format` fails on
`.agents/friction-log/20260831180632-immutable-releases-were/friction.md`.
That file already exists on `main` and is not touched here

Prompted by: @brendanjryan

Co-authored-by: Brendan Ryan <1572504+brendanjryan@users.noreply.github.com>

Author: decofe

.changelog/bump-mppx-0-12-0.md

@@ -0,0 +1,5 @@
+---
+wallet-cli: patch
+---
+
+Update `mppx` to 0.12.0 and `viem` to 2.57.1.

package.json

@@ -39,9 +39,9 @@
   "dependencies": {
     "accounts": "0.17.3",
     "incur": "0.4.20",
-    "mppx": "0.8.14",
+    "mppx": "0.12.0",
     "undici": "8.10.2",
-    "viem": "2.55.10"
+    "viem": "2.57.1"
   },
   "devDependencies": {
     "@types/node": "25.9.2",

pnpm-lock.yaml

@@ -8,3 +8,7 @@ allowBuilds:
 
 minimumReleaseAge: 10080
 trustPolicy: no-downgrade
+
+minimumReleaseAgeExclude:
+  - mppx@0.12.0
+  - viem@2.57.1