fix(agera,kida,nanoviews,query): run user reducers and event handlers untracked

[dangreen]

Two tracking barriers around code the library user writes, found by a repo-wide audit of untracked coverage.

• nextValue calls the reducer form of a signal write with tracking off, so $signal(value => value + $other()) no longer subscribes whatever effect performs the write; it also takes an extra argument to pass to the reducer
• route the query cache setter and kida child setter through nextValue instead of their own isFunction branches
• run delegated event handlers untracked: an event dispatched synchronously from an effect - element.focus() under autoFocus$ - no longer subscribes that effect to what the handler reads, which could steal focus back on every unrelated change

Every fix has a regression test that is red without it: signal.spec.ts (the core reducer), array.spec.ts (updateArray), cache.spec.ts ($data), effects.spec.ts (delegated events).

Measured along the way: rest parameters for the reducer argument are ~2.3x slower than a single optional one, so the signature takes one argument; pushActiveSub() without the explicit undefined is perf-neutral but costs bytes, so the call sites keep it.

Sizes: agera 2730 / 1345 / 1513 / 1927, kida 4188 / 1349 / 2273, nanoviews 6845 / 4044, store 5609 / 1349 / 2274 - the core barrier reaches every bundle because it sits in the single funnel of functional writes. Suites: agera 126 + 1 expected fail, kida 62, store 57, nanoviews 73, query 163, router 129.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.59%. Comparing base (244fafc) to head (39c5eec).

Files with missing lines	Patch %	Lines
...ackages/nanoviews/src/internals/elements/events.ts	77.77%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #193      +/-   ##
==========================================
+ Coverage   84.54%   84.59%   +0.05%     
==========================================
  Files         139      139              
  Lines        3112     3116       +4     
  Branches      580      578       -2     
==========================================
+ Hits         2631     2636       +5     
  Misses        343      343              
+ Partials      138      137       -1     

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