feat: add dodge roll mechanic (closes #338)

[harshaaaaw]

Summary

Implements a dodge roll mechanic for #338.

• Adds /datum/component/dodge which hooks COMSIG_MOB_APPLY_DAMAGE and returns COMPONENT_NO_DAMAGE while the mob is mid-dodge, so the player takes no damage during the roll.
• Adds a Dodge Roll IC verb (keybindable) with a short dodge window and cooldown.
• Includes a changelog entry.

Changes

• code/datums/components/dodge.dm: new component + verb
• html/changelogs/changelog_dodge.yml: changelog

Test plan

• A mob performing a dodge roll takes no damage from incoming attacks during the i-frame window.
• After the window, normal damage applies again; cooldown prevents spam.

Closes #338