Campaign progression: standard progress schema and shared campaign Lua boilerplate

Part 2 of #22600, depends on #22601. The state store holds arbitrary data; this milestone defines the small standard schema on top of it that engine UI and unlock logic can rely on, plus the shared Lua boilerplate that writes it — so every campaign records progress the same way without every mission reinventing it.

Design

• Standard keys in each mission document, written at mission end: at minimum completed (bool), difficulty, time, score, attempts. Everything else stays free-form alongside them. - OPEN TO DISCUSSION
• The defeat path records too (attempts, per-mission stats) — not just victory. Lua OnPlayerWon/OnPlayerLost triggers run before the world stops, so no engine changes are needed to record outcomes.
• A shared helper in the common campaign Lua (loaded before map scripts since #19968) does the recording, so a mission opts in with one call.
• Custom score metrics (e.g. "Commando died and respawned X times") remain possible as free-form keys next to the standard ones.

Work items

• Document the standard schema (key names, types, units — e.g. is time ticks or seconds)
• Shared Lua helper that records mission outcome (victory and defeat) into the store
• Wire it into one reference campaign's missions
• Decide and implement replay-from-browser semantics: proposal — re-playing an already-completed mission only ever improves the stored result (better time/score, higher difficulty), never regresses it
• Decide where difficulty is recorded, coordinating with #21698 (which proposes sharing the campaign save file for remembered lobby options)

Out of scope

Displaying any of this (milestone 3), the score screen itself (milestone 4).