Scopes what parse and compile refuse in the README

[johnnyt]

Bead: pts-d3ft

What changes

README only (an also-gated path, so the full gate ran).

• The decompile example's comment said parse refuses exactly what compile refuses. It now says parse refuses every source whose scan or grammar fails, with the refusal compile answers for that source, and that the converse does not hold: compile runs an emitter parse does not, and the emitter refuses a numeric literal the value domain cannot hold and a source its walk counts past the depth limit where the grammar's count stops short. A new executed check in the same block shows a library hold rule with an oversized literal parsing and being refused by compile with number_out_of_range.
• The Ast paragraph scopes the round-trip promise: for a source compile accepts, decompile(parse(source).ast) keeps answering what the reference answers for that source.
• The paragraph opening "Compiling an expression from its source text is compile" no longer says the statement grammar arrives in a later release. It names compileProgram and its two located siblings beside compile and its two, and says execute and executeValue run a source string as a statement program while evaluate compiles an expression, as src/index.ts and src/compile.ts do on main.
• The "The entry points" bullet for the main entry point is rewrapped to the wrap width of its neighbours.

Provenance

• The entry-points bullet also gains the statement program in its list (the compilation of a statement program's source text, and the run of a list), so the bullet describes the entry point as it is; beyond the rewrap the bead's note asked for.
• A second overlong line, in the paragraph after the decompile example, is rewrapped (whitespace only).

Checks

• Full gate (mise exec -- pnpm run gate) green on the committed tree; the README examples run under test/readme.test.ts.
• Two sabotage checks on the new example, each restored byte-equal: expecting a different reason for the compile refusal, and making the parsed source ungrammatical; each turned test/readme.test.ts red on the example's own thrown check.
• No changelog fragment: documentation only, per changelog.d/README.md.

Review

Own in-turn review round (gate tier): every new sentence was checked against src/index.ts (parse's doc comment, which names the two emitter-only refusals) and src/compile.ts on main, and the oversized-literal behaviour was run before it was written down.