perf: compact initial TailHTML fixups

[linkdata]

Closes #387

Summary

• emit one block-scoped fixup wrapper and only the A/R/C/D helpers used by each initial tail
• pass numeric Jid suffixes and reconstruct element IDs from jid.Prefix
• preserve raw operation payloads; only SAttr splits at its first newline
• isolate each operation, preserve missing-element and escaping behavior, and apply the WebSocket client's reserved-id guard
• preallocate from eligible operation, helper, and payload sizes
• serve the generated classic script explicitly as UTF-8
• cover helper selection and alias mapping without Node, and compare DOM effects and errors with the WebSocket dispatcher when Node is available

All non-empty tails use the alias form. One SClass("cls") fixup grows from 89 to 146 bytes; six comparable class fixups shrink from 534 to 201 bytes.

Measurements

Compared with origin/main using six one-second samples per version and benchstat. The timed loop includes queue refill and one-shot reset.

Fixture	Tail bytes	Time/op	B/op	Allocs/op
One fixup	89 → 146 (+64.0%)	193.6 → 155.6 ns (-19.7%)	224 → 160 (-28.6%)	3 → 1 (-66.7%)
300-operation board	32,120 → 9,196 (-71.4%)	108.19 → 40.23 µs (-62.8%)	154,336 → 10,240 (-93.4%)	18 → 1 (-94.4%)
100 long attributes	21,792 → 14,419 (-33.8%)	119.65 → 70.78 µs (-40.8%)	113,376 → 16,384 (-85.6%)	17 → 1 (-94.1%)

Verification

• go generate ./...
• go vet ./...
• gofmt -l .
• staticcheck ./...
• golangci-lint run
• gosec ./...
• go build ./...
• GOOS=linux GOARCH=386 CGO_ENABLED=0 go build ./...
• JAWS_REQUIRE_NODE=1 go test -race ./...
• JAWS_REQUIRE_NODE=1 go test ./...