Dev tools consistency: remove dark mode from velocity-playground and persist last query across query-tool, es-search, and velocity-playground

Description

Two consistency gaps across the migrated dev-tool portlets — dot-query-tool, dot-es-search, and dot-velocity-playground — that should be addressed together so the three portlets behave uniformly.

1. Remove dark mode from dot-velocity-playground

Only dot-velocity-playground ships a dark theme toggle; the other two dev tools do not. This creates an inconsistent UX across otherwise-sibling portlets. Remove the dark mode from dot-velocity-playground so all three follow the platform's default theming.

2. Persist the last query per portlet — homogeneous across the three

Users lose their in-progress work when they leave and return to any of these portlets. Dev-tool queries (Lucene, ES JSON, VTL) are complex and time-consuming to recompose, so the last query should be restored when the user comes back to the portlet.

Deliver a single, shared implementation used by all three portlets, backed by localStorage. dot-velocity-playground already persists splitter ratio and history via localStorage (readJson / writeJson utilities in dot-velocity-playground.utils.ts) — extract that pattern into a shared location and reuse it across the three portlets.

Suggested approach

• Promote the persistence utilities (or wrap them as a withPersistedQuery() SignalStore feature) into libs/data-access/ or libs/ui/ so all three portlets consume the same helper.
• Key naming convention: dotcms.devtools.{portlet}.lastQuery (e.g. dotcms.devtools.query-tool.lastQuery).
• Debounce writes (~300 ms) while the user is typing.
• Load and restore the last query on portlet init.
• Provide an explicit "Clear" action per portlet that removes the stored value.
• Per-portlet payloads:
  • dot-query-tool: Lucene query string (+ minimal filters if any).
  • dot-es-search: ES query JSON.
  • dot-velocity-playground: VTL body — reconcile with existing history/splitter storage, do not duplicate.

Acceptance Criteria

• Dark mode / dark theme toggle is removed from dot-velocity-playground (UI, config, and any related code paths).
• All three portlets (dot-query-tool, dot-es-search, dot-velocity-playground) render with the same default theming; no portlet-specific theme switch remains.
• A shared persistence helper exists in a shared lib (libs/data-access/ or libs/ui/) — not duplicated per portlet.
• Each of the three portlets restores the last query on load from localStorage.
• Each portlet saves the current query to localStorage on change (debounced ~300 ms).
• Each portlet exposes a "Clear" action that removes the stored value.
• Storage keys follow the convention dotcms.devtools.{portlet}.lastQuery.
• dot-velocity-playground existing localStorage usage (history, splitter ratio) is reconciled with the new helper — no duplicated storage for the same data.
• Unit tests cover: load-on-init, save-on-change (debounced), clear action, and corrupt / missing storage value handling.
• Manual QA: reload the browser after typing a query in each portlet and confirm the query is restored.

Priority

Medium — quality-of-life fix for power users of the dev tools; not blocking.

Additional Context

Existing persistence pattern to draw from: libs/portlets/dot-velocity-playground/src/lib/dot-velocity-playground.utils.ts (readJson, writeJson, HISTORY_STORAGE_KEY, SPLITTER_STORAGE_KEY).