feat: Simple / Aggregation / Shell query modes

[ByteExceptionM]

Add a three-way mode picker in place of the old redundant db.coll
header so each tab can be driven by one of:

• Simple — existing filter/sort/projection/limit/export
• Aggregation — single editor for an EJSON pipeline array, dispatched
  through a new query.aggregate IPC channel + QueryService method
• Shell — mongosh-flavoured one-liner like
  db.coll.find({…}, {…}).sort({…}).skip(n).limit(n) or
  db.coll.aggregate([…]); parsed in the renderer (new shellParser
  with 12 tests) and dispatched to the existing find / aggregate APIs

The mode picker uses an underline-indicator style flush against the
toolbar body, with Run / Limit / Export on the right of the same bar.
Active collection tab in the TabBar above gets a 2px primary top-border,
font-medium, and a tinted db. prefix so it's clearly distinguishable.

Other UX fixes bundled in:

• Run morphs into a destructive Cancel (X) while a query is in flight;
  click soft-cancels via queryClient.cancelQueries.
• Sort and Projection editors share their height — whichever's content
  is taller pushes the other to match (QueryEditor reports its natural
  content height; SimpleBody feeds max() back as both editors' minHeight).
• Switching tabs no longer re-runs the query: refetchOnMount: false +
  staleTime: Infinity on the active query. Initial open still fetches
  (no cache for that key).
• Run is always clickable when not loading; bumping a per-tab runEpoch
  on every Run guarantees a fresh fetch even when none of the
  mode-specific params changed.