Address PR review: panel sizing, credentials, fallback errors, opt-in logging

[pkamble-ks]

Summary

Addresses maintainer review feedback on upstream PR gnachman#682 (Keeper Nested Shared Folder support).

• New Account panel: Default height restored to 136px; expands to 196px only when the adapter declares an add-account toggle.
• Credentials: Removed keychain settings cache; restored login-credential precedence over settings keychain value.
• Adapter fallback: For unprefixed account IDs, only try the second Commander verb on not-found/wrong-type errors (preserve first meaningful error).
• addRecord: Validate record UID from structured fields (and message fallback) before returning.
• Logging: Opt-in via ITERM2_KEEPER_ADAPTER_LOG_ENABLED=1 (default off).
• Release notes: Replaced em dash with period per project style.

--force on add/update confirmed against live Commander Service Mode (see upstream PR comment).

Test plan

• cd pwmplugin && swift test --filter KeeperIntegrationTests (21/21)
• Manual: Bitwarden/KeePassXC Add Account panel (no extra gap)
• Manual: Keeper Add Account panel (toggle visible, panel expanded)