fix: add padId to padUpdate/padCreate hook context (#7452)

The pad object's toJSON() intentionally strips the id property (since
it's part of the database key), which caused confusion when plugins
serialized the hook context. Adding padId as a top-level property on
the hook context makes it directly accessible without relying on the
pad object's internal properties.

Fixes #5814

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/node/db/Pad.ts

@@ -125,6 +125,7 @@ class Pad {
       authorId && authorManager.addPad(authorId, this.id),
       hooks.aCallAll(hook, {
         pad: this,
+        padId: this.id,
         authorId,
         get author() {
           pad_utils.warnDeprecated(`${hook} hook author context is deprecated; use authorId instead`);