feat: Refactor helm chart

[amartingarcia]

What this PR does / why we need it:

Major modernization of the helm-steampipe chart — bringing it from a stale v1-era chart (appVersion: 0.22.0) to a fully audited, automated, and documented v3.0.0 chart targeting
Steampipe v2.4.1 with Powerpipe integration.

Structural changes:

• Restructured repo: charts/* → charts/steampipe/* (standard helm-releaser layout)
• Updated appVersion:
  0.22.0 → 2.4.1, version: 1.0.0 → 3.0.0

Bug fixes (v2 audit):

• Fixed ingress backend service name ($fullName → $fullName-psql)
• Removed steampipe mod install from init scripts (mods → Powerpipe in v2)
• Removed invalid STEAMPIPE_LOG_LEVEL env var (doesn't exist in v2)
• Cleaned up all dashboard volumeMounts/volumes (dashboard removed in v2)
• Fixed deployment args nesting bug (args only applied conditionally)
• Fixed oauth2-proxy dependency (10.1.3 → 10.4.2)
• Fixed updatecli helm-chart-dependencies.yaml (kind: dockerimage → kind: helmchart)

New features:

• Powerpipe integration: New deployment, service, and ingress templates for Powerpipe dashboards
• Added values.schema.json (JSON Schema validation for all chart values)
• Added 6 CI test values files (ci/values-*.yaml) for chart-testing
• Added TCP ingress warnings in docs and values for PostgreSQL compatibility

Automation:

• New helm-check-steampipe-release.yml workflow (daily cron via updatecli)
• New helm-check-powerpipe-release.yml workflow
• New powerpipe-appversion.yaml updatecli manifest
• Fixed helm-appversion.yaml target to kind: helmchart with versionincrement: patch
• Renamed helm-dependencies.yaml → helm-chart-dependencies.yaml
• Added npm ecosystem to dependabot.yml

Documentation:

• Complete rewrite of root README.md (logo, badges, architecture diagram, 5 real-world examples, plugins/mods tables, contributing guide)
• Complete rewrite of charts/steampipe/README.md.gotmpl (7 examples, migration guide v1→v2, environment variables reference, troubleshooting)
• Created TESTING.md (local testing guide)
• Created context7.json for Context7 indexing
• Created .pre-commit-config.yaml (helm-lint, helm-docs, trailing-whitespace, markdown-toc)

Files changed: 44 files, +2187 / -235

Which issue this PR fixes

• N/A — proactive modernization and v2 alignment

Special notes for your reviewer:

• This is a breaking change (v1.x → v3.0.0): chart directory moved, dashboard values deprecated, mods moved to Powerpipe
• The initContainer.mods value is deprecated with a note pointing users to Powerpipe
• Ingress for Steampipe (PostgreSQL/TCP) requires a TCP-capable controller (e.g., NGINX TCP passthrough, Traefik IngressRouteTCP) — standard HTTP Ingress won't work.
  Documentation includes warnings.
• Powerpipe templates are new and should be reviewed for correctness
• All changes validated with helm lint and helm template against all ci/values-*.yaml files