feat(dom): jQuery wrapper scaffold + dom/query module (Step 1)

[elnelson575]

Summary

First step of a long-term effort to wrap Shiny's jQuery usage behind a capability-oriented adapter layer. Lays the foundation; no user-facing API changes.

• New srcts/src/dom/ wrapper. Capability modules with native + jQuery adapters and per-call dispatch (window.jQuery is checked at each call; native is used when absent).
• First module: dom/query (select, closest, matches).
• JQueryRequiredError for code paths that genuinely need jQuery and find it absent (infrastructure for follow-on modules; not yet thrown).
• Build-time fence. srcts/build/_jquery.ts gains a second rule: import $ from "jquery" and JQuery<> type references are only allowed in srcts/src/dom/*/jquery.ts adapter files. A // shiny:jquery-allowed -- <reason> magic comment exempts pending files; every build prints a sorted audit of all 44 current exemptions so drift stays visible.
• One proof-of-concept migration. $(document).find("[data-display-if]") in shinyapp.ts switched to select(document, "[data-display-if]"). Behavior preserved (dispatch picks jQuery in production).
• Test infra. happy-dom added as devDep; setupDom() and withJQuery() helpers enable dual-path adapter parity tests. New tests: 12 parity (6 × 2 adapters) + 1 explicit no-jQuery regression + smoke tests for helpers/errors.

Design and plan are committed to the branch under .claude/specs/ and .claude/plans/.

Out of scope for this PR (deferred to follow-on PRs): dom/events, dom/html, dom/ajax, dom/widgets; the dual InputBinding/OutputBinding API; the package.json peer-dependency switch; migration of the 43 remaining jquery-importing files (each carries the escape-hatch comment for now).

Test plan

• npm run checks passes locally (lint, build_types, test_types, coverage, circular).
• npm run bundle_shiny succeeds and prints [_jquery audit] 44 file(s) carry shiny:jquery-allowed exemptions: at the end.
• npx tsx --test srcts/src/dom/query/__tests__/query.test.ts reports 12 passes (6 logical × 2 adapters).
• npx tsx --test srcts/src/dom/query/__tests__/query.no-jquery.test.ts passes with window.jQuery explicitly asserted undefined.
• Smoke a Shiny app that uses conditionalPanel() (which relies on the data-display-if selection we migrated) to confirm no regression in the conditional-show behavior.
• Inspect a deliberately-broken file by removing the shiny:jquery-allowed comment from any source file with import $ from "jquery" and confirm npm run bundle_shiny fails with the actionable Rule 2 error.

Notes for reviewers

• Known limitation: withJQuery() does not await async callbacks; the first follow-on plan (dom/events) will need to extend it before tests that use await will work correctly. Surfaced in the final code review on this branch; not blocking this PR because no current code path is async.
• dom/widgets future seam: JQueryRequiredError is the contract that the eventual dom/widgets module (jQuery-plugin widgets — datepicker, ion-rangeslider, selectize, DataTables) will throw when jQuery is absent. Defined here so adapter authors can rely on it.
• The single migration in shinyapp.ts is intentionally narrow — the goal is to prove the dispatch works end-to-end, not to drain the queue.