chore(pnpm): drop dead .pnpmrc, declare pnpm defaults in pnpm-workspace.yaml

pnpm v11 reads settings from pnpm-workspace.yaml (and the npm-compat
subset from .npmrc), not from .pnpmrc. The .pnpmrc file previously
committed was being silently ignored — every setting in it was a
no-op.

Changes:
- Delete .pnpmrc (dead file, pnpm does not read it).
- Append to pnpm-workspace.yaml:
  - autoInstallPeers: true     pnpm default, declared explicitly
  - enablePrePostScripts: true pnpm default, declared explicitly (husky)
  - saveExact: true            pin exact on `pnpm add`

No behavioral change — these match current pnpm defaults. Declaring
explicitly hardens against future pnpm default flips silently
diverging across the fleet.

Author: jdalton

.pnpmrc

@@ -85,3 +85,16 @@ trustPolicy: no-downgrade
 trustPolicyExclude:
   - '@yarnpkg/core@4.5.0'
   - '@yarnpkg/libzip@3.2.2'
+
+# Auto-install missing peer deps (pnpm default). Declared explicitly
+# so a future default flip can't silently change install behavior.
+autoInstallPeers: true
+
+# Run pre/post lifecycle scripts on the workspace root (e.g.
+# prepare -> husky). This is the pnpm default; declared explicitly
+# so a future default flip can't silently disable husky setup.
+enablePrePostScripts: true
+
+# Pin exact versions on `pnpm add`. Catalog and overrides should
+# also be exact pins (5.24.0, not ^5.24.0).
+saveExact: true