refactor(lua): move achievement tracking onto hooks

[scarf005]

Purpose of change (The Why)

Achievement tracking duplicated the existing Lua hook pipeline. Moving transition logic to Lua keeps the save payload unchanged while removes the per-achievement C++ watcher layer.

Describe the solution (The How)

• add an on_stat_changed hook and a core Lua achievement runtime that evaluates completion and failure
• keep achievements_tracker as the save/UI wrapper and pre-activate the required statistics without per-achievement watcher objects
• add regression coverage for achievement completion and serialized tracker state

Testing

• cmake --build --preset linux-full --target astyle
• cmake --build --preset linux-full --target cataclysm-bn-tiles cata_test-tiles
• ./out/build/linux-full/tests/cata_test-tiles "[stats]"
• ./out/build/linux-full/src/cataclysm-bn-tiles --check-mods (fails on unrelated local Backrooms-CBN-mod external option parsing error)

Checklist

Mandatory

• I wrote the PR title in conventional commit format.
• I ran the code formatter.
• I linked any relevant issues using github keyword syntax like closes #1234 in Summary of the PR so it can be closed automatically.
• I've committed my changes to new branch that isn't main so it won't cause conflict when updating main branch later.

Optional

• This PR modifies lua scripts or the lua API.
• I have added lua scope to the PR title.
• I have added type annotations to functions so that it's safe and easy to maintain.

^{PR opened by gpt-5.4 high on opencode}