test(devnet): add LEP-6 chain-side lifecycle e2e tests

[j-rafique]

Closes the missing devnet-test gap for LEP-6 storage-truth (Anton: 'LEP-6 doesn't even have devnet tests'). Chain-side lifecycle e2e under the live 5-validator Docker devnet, modeled on devnet/tests/everlight/everlight_test.sh.

Tests (4, all chain-side, no supernode runtime dependency):
T1 TestLEP6_ParamsAndEpochAnchor — params readback, divisor/mode/epoch_length
sanity, current-epoch-anchor query, active SN set check.
T2 TestLEP6_SubmitEpochReport_HappyPath — host report + peer observations +
storage proof results submitted by prober; storage-challenge-reports query
confirms indexed.
T3 TestLEP6_SubmitStorageRecheckEvidence_UpdatesSuspicionScore — INVALID_TRANSCRIPT
seed -> RECHECK_CONFIRMED_FAIL; verifies +15 NodeSuspicion delta and +8
TicketDeterioration delta (LEP-6 spec scoring constants).
T4 TestLEP6_HealOpLifecycle_ClaimVerifyFinalize — drives ticket deterioration
past heal_threshold via repeated rechecks, EndBlock creates heal op,
claim-heal-complete + submit-heal-verification x2 -> HEAL_OP_STATUS_VERIFIED.

Files:

• new: devnet/tests/lep6/lep6_test.sh (1062 lines, bash)
• new: docs/plans/LEP6_DEVNET_TEST_PLAN.md
• mod: devnet/default-config/devnet-genesis.json (5 LEP-6 param tweaks for testability: divisor=1, mode=SOFT, postpone_threshold=100, decay=1000 (no decay), consecutive_epochs_to_postpone=100; epoch_length_blocks=20 was already present)
• mod: Makefile.devnet (devnet-tests-lep6 target + .PHONY)
• mod: devnet/Readme.md (§6.7 table — adds everlight + lep6 rows)

Self-bootstrap registration: devnet bundle ships only lumerad + libwasmvm (no supernode binary), so supernode-setup.sh skips. Test self-registers each validator's own key as a supernode if no SNs exist (mirrors everlight_test.sh:ensure_supernode_registered_for_service).

Validation: 15/15 PASS, 0 FAIL, 0 SKIP against live 5-validator devnet (2026-05-03). All LEP-6 spec scoring constants verified end-to-end under real BFT consensus.

Out of scope (follow-up PRs):

• Full supernode<->lumera e2e (gated on supernode #286/#287/#288 merge)
• Postponement / recovery / edge cases (already covered in tests/systemtests/audit_storage_truth_*)
• devnet-upgrade-1120 rehearsal target (separate concern)

Note for everlight_test.sh maintainer: S7.7's 'set epoch_length_blocks=20 via gov' is now redundant — the param became genesis-immutable upstream and this PR makes the genesis ship at 20.

Run with:
make devnet-up-detach
make devnet-tests-lep6