docs(ui): document input setter dirty-tag requirement

[linkdata]

Summary

• define the setter-derived dirty-target contract on ui.Input
• link all eight interactive input constructors to that contract
• expand the README data-binding guidance with a realistic validating setter
• explain rejected and normalized browser behavior and why render-param tags do not substitute
• keep the JaWS contributor skill guidance aligned

Closes #237

Stack

Depends on #242 because both changes edit the same documentation files. This branch contains one issue-237 commit on top of that PR.

Verification

• go doc for ui.Input and all eight constructors
• go generate ./...
• go vet ./...
• gofmt check
• staticcheck ./...
• golangci-lint run
• gosec ./...
• JAWS_REQUIRE_NODE=1 go test -race -coverprofile=/tmp/jaws-237-coverage.out ./...
• JAWS_REQUIRE_NODE=1 go test ./...
• go build -v ./...
• Linux/386 lib/bind test binary cross-compiled successfully; darwin/386 execution is unsupported by the local Go toolchain