feat: implement multitenancy with tenant isolation + environment support

Adds configurable tenant ID (CAMELEER_TENANT_ID env var, default:
"default") and environment as a first-class concept. Each server
instance serves one tenant with multiple environments.

Changes across 36 files:
- TenantProperties config bean for tenant ID injection
- AgentInfo: added environmentId field
- AgentRegistrationRequest: added environmentId field
- All 9 ClickHouse stores: inject tenant ID, replace hardcoded
  "default" constant, add environment to writes/reads
- ChunkAccumulator: configurable tenant ID + environment resolver
- MergedExecution/ProcessorBatch/BufferedLogEntry: added environment
- ClickHouse init.sql: added environment column to all tables,
  updated ORDER BY (tenant→time→env→app), added tenant_id to
  usage_events, updated all MV GROUP BY clauses
- Controllers: pass environmentId through registration/auto-heal
- K8s deploy: added CAMELEER_TENANT_ID env var
- All tests updated for new signatures

Closes #123

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

deploy/base/server.yaml

@@ -99,6 +99,8 @@ spec:
               value: "clickhouse"
             - name: CAMELEER_STORAGE_EXECUTIONS
               value: "clickhouse"
+            - name: CAMELEER_TENANT_ID
+              value: "default"
 
           resources:
             requests: