Surface StorageVersionMigrator behind chart feature flag (opt-in)

[ChrisJBurns]

Summary

Exposes the StorageVersionMigrator controller (PR-A, #5362) to operator users via a new helm chart feature flag.

The feature stays opt-in via the chart value (default false). Admins who want auto-migration set operator.features.storageVersionMigrator: true at install or upgrade time. A future release can flip the default if/when we want the feature on by default — that flip is intentionally a separate decision.

User-facing reference docs and the upgrade-guide walkthrough are deliberately not in this PR — they land separately.

Part of #4969. Depends on #5362 (merged) and #5391 (merged).

Medium level

• New operator.features.storageVersionMigrator value in deploy/charts/operator/values.yaml, defaulting to false. helm-docs comment explains what the feature does — no temporal claims about when the default might change.
• deployment.yaml wires TOOLHIVE_ENABLE_STORAGE_VERSION_MIGRATOR env var from the chart value.
• deploy/charts/operator/README.md regenerated by task helm-docs to reflect the new value.
• No operator-code change. The default in cmd/thv-operator/app/app.go's isStorageVersionMigratorEnabled() stays false — chart-level opt-in is sufficient for helm-installed operators, and keeping the operator-code default unchanged matches PR-A's posture.

Low level

File	Change
deploy/charts/operator/values.yaml	New operator.features.storageVersionMigrator: false value (+6 lines)
deploy/charts/operator/templates/deployment.yaml	New env-var block wiring TOOLHIVE_ENABLE_STORAGE_VERSION_MIGRATOR (+2 lines)
deploy/charts/operator/README.md	helm-docs regeneration (+2 / -1)

Type of change

• New feature (additive — extends an existing env-var-driven feature flag with a chart-level surface)
• Bug fix
• Breaking change
• Refactoring
• Documentation
• Other

Test plan

• task build clean
• helm lint deploy/charts/operator clean
• task helm-docs produces no further diff after the value is added
• TOOLHIVE_ENABLE_STORAGE_VERSION_MIGRATOR env var wiring matches the constant the controller reads in cmd/thv-operator/app/app.go

Why default false

Opt-in posture for one release:

• Lets operators try the feature on staging before flipping their production charts.
• Avoids the situation where users on helm upgrade get a behavioural change they didn't anticipate.
• Defers the "feature must be on for the version-removal release to be safe" coupling to a deliberate later flip, when the upgrade story is more visible to users.

A future release will flip the chart default to true. That flip is intentionally a separate decision.

Follow-ups (separate PRs / issues)

• User-facing reference docs and upgrade-guide walkthrough (will land in a follow-up PR).
• Operator-code default flip in app/app.go (paired with the chart-default flip).
• Chart-conditional RBAC gating (template the migrator's RBAC rules behind if .Values.operator.features.storageVersionMigrator).
• CRD-level MigrationStuck Condition + Warning event for better SRE visibility.
• Full Prometheus metrics suite (crs_processed_total, reconcile_duration_seconds, cache_size, consecutive_conflict_passes).

Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.77%. Comparing base (05ca226) to head (cf9c977).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5418      +/-   ##
==========================================
+ Coverage   68.76%   68.77%   +0.01%     
==========================================
  Files         629      629              
  Lines       63937    63937              
==========================================
+ Hits        43964    43972       +8     
+ Misses      16721    16712       -9     
- Partials     3252     3253       +1     

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