feat(database): finalize operational schemas

[MagicTheDev]

Summary

• remove the rejected CWL-only cwl_season_statistics surface in forward migration 016 while retaining canonical CWL and war storage
• finalize battle storage in migration 017 with numeric mode/direction codes, non-null smallint durations, canonical share codes, and no hashes or compatibility columns
• replace parallel aggregate schemas with unsuffixed day/cohort totals for legend_i, top_1000, and top_200
• compact current/daily leaderboard storage, move notification categories and timings to user scope, and enforce verified-link account ownership
• migrate bases to bigint identities with relational images, private votes/public counts, and retry-safe first-click enrichment
• retain migration 018 unchanged in history, then supersede its numbered slots in migration 019 with unlimited user_saved_bases rows and nullable text war|legend labels
• move lifetime first-download identity onto bases.downloads as an immutable Discord-user-to-ISO-timestamp JSON object, migrate existing timestamps, drop base_downloaders, and count unique JSON keys
• remove obsolete hash contracts and cleanup tooling, and document exact Tracking/API/Bot/Dashboard/App contracts

Validation

• goose -dir database/timescale validate
• go test ./... from database/
• clean disposable Timescale 001 -> 019: bash ../scripts/with-test-timescale.sh --profile retained-api -- env GOCACHE=/tmp/clashking-schemas-go-cache go test ./schema ./migrations -count=1
• data-bearing disposable Timescale 013 -> 019: bash ../scripts/with-test-timescale.sh --profile baseline-013 -- env GOCACHE=/tmp/clashking-schemas-go-cache go test ./schema -run '^TestArmyCodeFamilyCompatibilityMigration$' -count=1 -v
• populated personal-base Timescale 018 -> 019: bash ../scripts/with-test-timescale.sh --profile baseline-018 -- env GOCACHE=/tmp/clashking-schemas-go-cache go test ./schema -run '^TestPersonalBaseStorageMigration$' -count=1 -v
• node --test scripts/with-test-timescale.test.mjs
• env GOCACHE=/tmp/clashking-schemas-go-cache bash scripts/validate-repository.sh
• actionlint .github/workflows/schema-upgrade.yml
• git diff --check

Rollout boundary

This PR does not deploy or apply migrations. Migration 017 and migration 019 are irreversible and require coordinated final Tracking/API/Bot/App consumers before production execution. Migration 019 must be present before the API/App unlimited personal-base contract ships. Aggregate rows are rebuilt from retained raw attacks because the prior tables do not contain the final cohort/day semantics.

Migration 019 SQL SHA-256: 892a3639391311c0d34348be5679fdb1f7a70ce2cbf82fc3181d3a35e4aff11d.

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