sharing 7/7: Game modes export (widget, headless startscript, CI workflow)

[keithharvey]

📚 Stacked split of #5704 — review bottom-up

• 1/7 · Transfer library (enums, comms, serialization, test infra) (sharing 1/7: Transfer library (enums, comms, serialization, test infra) #8125)
• 2/7 · Modes & economy boundary (presets, waterfill, share ledger) (sharing 2/7: Modes & economy boundary (presets, waterfill, share ledger) #8126)
• 3/7 · Policies (context → policy → policy_result → action) (sharing 3/7: Policies (context → policy → policy_result → action) #8123)
• 4/7 · Transfer runtime (controllers, economy boundary, gadget swap) (sharing 4/7: Transfer runtime (controllers, economy boundary, gadget swap) #8062)
• 5/7 · Tech Core / Keystone (sharing 5/7: Tech Core / Keystone #8063)
• 6/7 · Sharing Tab UI (sharing 6/7: Sharing Tab UI #8064)
• 7/7 · Game modes export (widget, headless startscript, CI workflow) (sharing 7/7: Game modes export (widget, headless startscript, CI workflow) #8095) ← you are here

Each PR merges into the one below it; together they reproduce the sharing_tab branch (bar one intentional change — index.lua lazy-loads the mode helpers).

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Stack 7 of 7 splitting #5704. Builds on 6/7.

Game-modes export tooling, split out of Foundations since it depends on every mode/modoption the earlier parts define and is consumed entirely out-of-engine:

• Widget export_game_modes.lua — headless /exportgamemodes widget; reads modes/<category>/* over modoptions.lua defaults, emits game_modes.json (schemaVersion 1) for out-of-engine consumers (the SPADS ModeCommand plugin)
• startscript_modes_export.txt — runs the widget headless, then quits
• CI export_game_modes.yml — regenerates + publishes to a rolling game-modes prerelease: push (stable/master) → per-channel game_modes-<channel>.json (stable/test); workflow_dispatch → commit-pinned game_modes-<shortsha>.json for off-master test builds (channel assets untouched, pruned to newest 50)

[github-actions]

Integration Test Results

18 tests   9 ✅  20s ⏱️
 1 suites  8 💤
 1 files    1 ❌

For more details on these failures, see this check.

Results for commit 0bb62a9.

♻️ This comment has been updated with latest results.