fix: Start-TssSecretChangePassword defaults -Type to 'Random' (#444)

[jagger]

Summary

Removes [Parameter(Mandatory)] from -Type and sets its default to 'Random'. The most common call - an immediate random password rotation - is now:

Start-TssSecretChangePassword -TssSession $s -Id 46

instead of the previously required -Type Random boilerplate.

Adds a second .EXAMPLE showing the Manual-with-supplied-password path so the non-default usage is still easy to find.

Closes #444.

Behavior matrix

Unchanged from what the issue requested:

-Type	-NextPassword	Result
(omitted)	(omitted)	Random rotation (new default)
Random	(omitted)	Random rotation (explicit, same as before)
Manual	provided	Manual rotation
Manual	(omitted)	Error: -NextPassword required (unchanged)
Random	provided	Error: -NextPassword cannot be used with Random (unchanged)

Lab verification

Against Secret Server 12.x:

=== Call without -Type (should default to Random) ===
POST .../internals/secret-detail/86509/change-password-now with:
  { "data": { "PasswordType": 0, "NextPassword": null } }
Password Change successfully started on Secret [86509]

=== Call with -Type Manual but no -NextPassword (should error gracefully) ===
-NextPassword parameter must be provided when using PasswordType of [Manual]

Both paths behave as specified.

Release

Targets v0.62.1 (on the 0.62.1 milestone). UX change with no API surface removal - callers who were explicitly passing -Type Random continue to work identically.

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