refactor: split axonopsplatform_controller.go into component files (3618 lines)

[digiserg]

Summary

internal/controller/axonopsserver_controller.go is 3618 lines with nolint:gocyclo. The Reconcile method alone spans ~380 lines. This makes testing, reviewing, and maintaining the code prohibitively expensive.

Proposed split

New file	Functions to move
timeseries.go	reconcileTimeseries, ensureTimeseriesStatefulSet, buildTimeseriesEnv, cleanupInternalTimeseriesResources
search.go	reconcileSearch, ensureSearchStatefulSet, buildSearchEnv, cleanupInternalSearchResources
server.go	reconcileServer, ensureServerStatefulSet, ensureServerConfigSecret, buildServerConfig, buildServerEnv, server ingress/gateway functions
dashboard.go	reconcileDashboard, ensureDashboardDeployment, ensureDashboardConfigMap, dashboard ingress/gateway functions
credentials.go	ensureAuthenticationSecret, ensureKeystorePasswordSecret, generateRandomPassword, getSecretKeys, shouldRetainCredentials
tls.go	ensureTLSCertificate, ensureClusterIssuer
helpers.go	buildLabels, buildSelectorLabels, ptr, resolveInitImage, resolveImage, shared service/SA functions

Acceptance Criteria

1. No file > 800 lines
2. axonopsserver_controller.go contains only the Reconciler struct, Reconcile method, and SetupWithManager
3. All functions remain in the same Go package (controller)
4. All existing tests pass without modification
5. make lint passes (no new issues)

Priority

P1

[digiserg]

Note: Following the rename in #106, the target file is now internal/controller/axonopsplatform_controller.go (renamed from axonopsserver_controller.go). All proposed split filenames should use the axonopsplatform_ prefix.