tech-debt J: Delete the dead `toc-file` action input and correct the docs that promise any language code works

[mmcky]

toc-file is declared in action.yml, documented with a default in docs/user/action-reference.md:60, parsed into ActionInputs.tocFile, and asserted by a unit test — and read by nothing. grep -rn "\.tocFile" src/ | grep -v __tests__ returns nothing. The published Action interface has 11 documented inputs and one of them is a lie.

Delete it; do not wire it. Found independently by four separate audit passes.

Also: two user docs promise that any language code works, while the action throws on anything but zh-cn/fa/fr.

Findings covered

6 audit findings land here. F<n> are stable references into the audit; rank is the report ordering (1 = act first of 139).

• F12 · rank 58 · low · t/t — toc-file is a fully dead input: declared, documented, parsed, typed, unit-tested, zero consumers
• F67 · rank 59 · low · t/t — The published input reference advertises toc-file as a working knob
• F71 · rank 60 · low · t/t — The same input, delete-don't-wire framing
• F102 · rank 61 · low · t/t — The same input, silently overridden by a hardcoded _toc.yml
• F128 · rank 62 · med · s/s — The same input, advertised with a default, wired to nothing
• F126 · rank 131 · med · s/s — Three user docs promise any language code works; getInputs() throws on anything but en/zh-cn/fa/fr

Plan

Estimate 9h · Rebuilds dist-action/ yes · Wave 1, PR J

Dead inputs. F12 + F67 + F71 + F102 + F128 — delete toc-file from action.yml, ActionInputs, inputs.ts, the default-pinning test and the docs row; F126 correct the three docs that promise any language code works

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_{From the technical-debt audit of 2026-07-23 (141 candidates adversarially verified, re-validated against v0.23.0, 139 live). Effort is stopgap / full — t≈0.5h, s≈3.5h, m≈11h, L≈28h. Items marked ½ were partially addressed by v0.22.0/v0.23.0.}