spec: status lines for every section that landed ahead of its implementation (#539)

[gafferongames]

Closes #539. Docs only: docs/SPEC.md and docs/SPEC-TABLES.md. No rule
changes and no code.

Several specification sections state present-tense behavior the tree does not
carry. Each now says so in the house form §3.3, §6.6 and §2.9 already use: the
behavior is specified ahead of its implementation, what the tree does today,
and the issue that owes it. Every line is deleted by the implementation PR
that lands the behavior.

Each present-state sentence below was confirmed against the tree, with a probe
unit through schema check where the claim is a refusal.

site	what the tree does today	owed
SPEC.md §3.1	the scanner lexes /// as an ordinary // line comment and discards it, no Doc field exists in internal/ast or ir, and none of §4.1's misplacement refusals fires: a /// above package and a /// trailing a field both compile	#523 ruling 4
SPEC.md §4.2	internal/check gathers tags on *ast.TypeDecl alone. A field's pipe draws "unknown attribute", a table and a union declaration draw "takes no qualification", a const draws its own, a union arm's pipe draws "expected a field type", and a qualified enum or flags variant does not parse	#523 ruling 4
SPEC-TABLES.md §8.1	no target emits doc, num_tags or tags on TableFieldInfo or TableTypeInfo, and nothing upstream exists to fill one	#523 ruling 4
§6.5, §7, §19.2	TableRefuseReason is spelled in no target, no runtime and no tool. Open is const Scene * SceneOpen( const void * bytes, uint64_t length ), BlockOpen returns a bare bool, a measure answers a bare -1, and the name is not claimed, so a unit may declare it	#523
§4	no report struct carries a widened member. Any kind difference is one kind_mismatch and the payload is skipped, so the counters a caller sees are unknown, kind_mismatch, clamped, duplicate and malformed	#523
§2.4, §11	schema check accepts [E.Max]T in a table body with no diagnostic and exit 0	#540

docs/VERSIONING.md needs nothing from this branch: #536 landed the
[E.Max]T entry in its "Owed before 3.0.0" list, keyed to #540, and the
///-and-tags entry beside it. Rebased onto that, so the one owed entry per
site is main's.

go test ./compiler/ -run Doc passes, which is the gate that parses the
pages' own schema blocks.

🤖 Generated with Claude Code