JS WAM: string_length/2 and writeq/~q nested quoting

[s243a]

D34 residuals on the JS WAM string tag: string_length/2 and writeq/1 / recursive ~q quoting.

Branched from grok/wamjs-string-tag and extended it (net additions). No INTEGRATION_PATCH.md.

What landed

• string_length/2 — accepts a string, atom, or number (text form); binds the Unicode code-point length. string_length("abc", N) → N = 3.
• writeq/1 registered. The quoted writer (quoted_term_to_string) is the same path format ~q uses. It now recurses through lists and compounds:
  • strings render double-quoted: writeq("ab") → "ab"; writeq(["ab", foo]) → ["ab",foo]
  • atoms quote only when needed (see subset)
• write/1 is unchanged (string text unquoted; list spacing still ", ").

Atom-quoting subset (SWI-like, pragmatic)

Unquoted: [], !, ;, {}, ^[a-z][A-Za-z0-9_]*$, and ISO graphic atoms (#$&*+-./:<=>?@^~\) except the lone atom . (end-of-term). Quoted otherwise; escapes \\ and \' only.

Tests (local, all green)

1. tests/test_wam_javascript_builtins.pl including probe_string_polish and string_polish_output
2. tests/test_wam_javascript_lowered.pl and tests/test_wam_javascript_fact_sources.pl
3. Official CONFORMANCE_TARGETS=javascript harness exits 0 (adapter still unpatched; local 48-query stand-in stays 48/48)
4. SWI vs Node dumps match for string_length, writeq (string / quoted atom / bare atom / []), write of a string, and nested ~q

Residuals (unchanged / documented)

• Compiled "foo" literals still collapse to atoms (wam_target.pl out of scope)
• Fact-source cells stay atoms
• No \n/\t escapes in writeq
• Brace terms {a} not special-cased