P0.1+P0.2: Quota model changes & remove dead feature flags

[fupelaqu]

Phase-0 foundation of the pricing-repackaging epic (combined stories P0.1 + P0.2, elasticsql core).

P0.1 — Quota model changes

• Remove maxConcurrentQueries from the Quota case class (it was never enforced).
• Final Quota shape: Quota(maxMaterializedViews, maxQueryResults, maxClusters = Some(0), maxJoins = Some(0)) (4 args).
• Community tier rebalanced: maxJoins 1 -> 2, maxMaterializedViews 3 -> 1.
  • Community = { MV Some(1), results Some(10000), clusters Some(1), joins Some(2) }.
• Drop the max_concurrent_queries row from SHOW LICENSE output (ADR D1).

P0.2 — Remove dead feature flags

• Remove UnlimitedResults and AdvancedAggregations from the Feature enum (values / fromString / toSnakeCase).
• Result-limit policy is now driven solely by Quota.maxQueryResults per tier (no feature flag) — covered by the new ResultLimitInvariantSpec.
• Feature.values = [MaterializedViews, JdbcDriver, AdbcDriver, FlightSql, Federation, Repl] (size 6).

Verification

• + sql/compile, + core/compile (cross 2.12 + 2.13) green.
• licensing suites (QuotaSpec, FeatureSpec, FeatureFromStringSpec, LicenseManagerSpec, LicenseKeySpec, LicenseUsageSpec, ResultLimitInvariantSpec) — 82 tests pass.
• core LicenseExecutorSpec — 13 tests pass.
• scalafmtAll + headerCheck clean.
• licensing + core publishLocal'd at 0.20-SNAPSHOT (2.12 + 2.13) to unblock downstream P0.3/P0.4/P0.5/P0.6.

Docs/marketing deferred to P1.3 (no doc sync in this PR).

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