sharing 3/7: Modes & economy boundary (presets, waterfill, share ledger)

[keithharvey]

📚 Stacked split of #5704 — review bottom-up

• 1/7 · Policies (context → policy → policy_result → action) (sharing 3/7: Policies (context → policy → policy_result → action) #8123)
• 2/7 · Transfer library (comms, serialization, types, test builders) (sharing 2/7: Transfer library (comms, serialization, types, test builders) #8061)
• 3/7 · Modes & economy boundary (presets, waterfill, share ledger) (sharing 3/7: Modes & economy boundary (presets, waterfill, share ledger) #8124) ← you are here
• 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)

Each PR merges into the one below it; all seven squash-equal the sharing_tab branch (verified byte-identical).

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Stack 3 of 7 splitting #5704. Builds on 2/7.

The sharing-mode presets and the economy boundary the policies consume:

• modes/sharing/* presets (enabled, disabled, easy_tax, customize), sharing_mode_enums / helpers, modoptions.lua entries, types/Mode.lua
• economy/* — waterfill solver, manual share ledger, shared_config
• mode + economy specs

[github-actions]

Integration Test Results

14 tests  ±0   6 ✅ ±0   3s ⏱️ ±0s
 1 suites ±0   8 💤 ±0 
 1 files   ±0   0 ❌ ±0 

Results for commit 84cfbd0. ± Comparison against base commit 4ad5fe3.

[keithharvey]

Not actually merged — GitHub auto-closed this as "merged" when a base-branch force-push made the base contain this branch. Reordered + replaced by #8126 (Modes & economy, 2/7).