Tighten SelectLockLabors input handling and refresh viewscreen; rename docs

[unboundlopez]

Motivation

• Prevent invalid or unexpected entry_count values from being used by centralizing parsing and enforcing a minimum positive integer.
• Improve reliability of simulated GUI input by refreshing the current viewscreen reference before each input step.
• Make the overlay filename and documentation follow project naming conventions by removing the leading z from the doc file.

Description

• Add sanitize_entry_count(count, fallback) to parse and clamp numeric input to >= 1 and use it as the single source of truth for entry validation.
• Call sanitize_entry_count at the start of simulate_actions and in the EditField on_change handler, and initialize the edit field text with tostring(self.entry_count).
• Cache dfhack.gui.getCurViewscreen() into a local viewscreen variable inside the simulation loop and when scrolling back up so each gui.simulateInput uses a fresh viewscreen reference.
• Rename docs/zSelectLockLabors.rst to docs/SelectLockLabors.rst and update the intro to reference SelectLockLabors.

Testing

• No automated tests were run for this change.

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Codex Task