[P3] scripts/prune-stale-branches.sh lives in scripts/ — mixed-purpose directory

[itsmiso-ai]

Ask: Move scripts/prune-stale-branches.sh out of scripts/ into a directory reserved for non-GDScript tooling (scripts/bin/, scripts/ops/, or tools/) so the scripts/ directory strictly holds .gd files.
Expected files: scripts/prune-stale-branches.sh, scripts/bin/prune-stale-branches.sh (new path), docs/branch-cleanup.md

Problem: scripts/prune-stale-branches.sh is a bash script that prunes merged and stale generated local branches. It lives alongside the .gd files that make up the game's runtime modules (colony_sim.gd, game_state.gd, etc.). The scripts/ directory is otherwise exclusively .gd files; mixing shell tooling in there muddies the boundary between runtime code (loaded by Godot via preload and load) and out-of-band operator scripts (run manually or by CI). The README and root .gitignore treat scripts/ as the GDScript surface; an editor configured to "show Godot files in scripts/" would not match the bash script. A future tooling commit that adds another script (e.g. backfill-saves.sh) will most likely land in scripts/ too, entrenching the mixed-purpose directory.

Evidence:

• scripts/prune-stale-branches.sh — bash script with set -euo pipefail, executed manually via ./scripts/prune-stale-branches.sh
• ls scripts/ — 12 entries, 11 .gd files (colony_sim.gd, colony_stance.gd, constants.gd, goal_progression.gd, goal_reward.gd, game_state.gd, layout_math.gd, main.gd, milestone_manager.gd, rotating_goal.gd, tile_render.gd, worker_cap_logic.gd, worker_renderer.gd) and 1 bash script (prune-stale-branches.sh)
• docs/branch-cleanup.md — companion doc that documents the script's intent; locate references and update them in the same PR
• grep -rn "prune-stale-branches" — the script is only referenced in docs/branch-cleanup.md

Acceptance:

• scripts/prune-stale-branches.sh moved to scripts/bin/prune-stale-branches.sh (or tools/); scripts/ now contains only .gd files (and .uid files alongside them)
• docs/branch-cleanup.md updated to reference the new path
• Any CI or cron mention of the old path updated (none found currently)
• ls scripts/ and git status show the move cleanly without orphaned references