feat: Settings page for the log path + poll interval

[GabrielBBaldez]

Today the plugin auto-detects the first errors-ai.log in the project and polls on a fixed interval. Add a small Settings page so a user can point it at a specific file and tune the poll — useful in multi-module projects or when the log lives under build/.

What to do

In the :plugin module:

1. Add a PersistentStateComponent (project-level) holding two fields: logPath (empty = auto-detect, the current behavior) and pollSeconds (default = whatever StacktalePanel uses today).
2. Add a Configurable (registered via <projectConfigurable .../> in plugin.xml, under a "Stacktale" entry) with a text field for the path and a spinner for the interval.
3. Make StacktalePanel read these: if logPath is set, use it; otherwise keep auto-detecting. Apply pollSeconds to the existing poll.

Keep the defaults exactly matching today's behavior so existing users notice nothing until they change a setting.

How to verify

./gradlew runIde, open Settings → Tools → Stacktale, set a path, and confirm the tool window reads that file; clear it and confirm auto-detect returns. ./gradlew test green.

Files: a settings state class + a Configurable under plugin/src/main/java/.../idea/, plugin.xml, and a small change in StacktalePanel.

[kycasdzxc]

Picking this up👍