fix(llm): stop leaking instruction prompts instead of processed text

Running a custom instruction (translate, summarise, rewrite, explain code,
free prompt) inserted the instruction's own wording instead of the result.
Two faults stacked:

The instruction was passed as the text to process, leaving the system-prompt
argument empty. `BASE_SYSTEM_PROMPTS` has no `custom` key, so resolution fell
back to `refine` without saying so, and the model dutifully polished the
instruction it had been handed. The transcript never reached it.

And only `{{text}}` was substituted, which none of the five built-in
instructions use — they carry `{{targetLanguage}}`, `{{userPrompt}}`, or no
placeholder at all. The substitution was a no-op from the day it was written:
the presets landed ten hours before the code that expected them.

- Instruction prompts now go to the system-prompt argument and the transcript
  to the text argument. Instructions that spell out `{{text}}` keep their old
  meaning, so hand-written ones still work.
- `renderInstructionPrompt` resolves `{{text}}`, `{{userPrompt}}` and
  `{{targetLanguage}}` in one place, and warns by name when a placeholder is
  left standing rather than letting it reach the model.
- `resolveSystemPrompt` no longer drops silently to `refine` for `custom`.
- Voice shortcuts no longer die at the `defaultLLMAction === 'none'` gate; an
  explicitly named instruction outranks the default. Without one, `none` still
  passes the transcript through untouched.
- `translate` receives its target language instead of relying on a default two
  call frames away. It is still always English — `AppConfig` has no key for it,
  and neither `language` (UI locale) nor `sttLanguage` (source language) can
  stand in. Choosing a target language needs a setting and is not in this fix.
- Chains ran instructions with placeholders intact; they share the same
  resolution now.
- The command screen's pipeline bench called `llm.generate`, which preload does
  not expose, so every run threw and the catch showed the input back as if it
  had succeeded. It uses `llm.process` now, over the same path production
  takes, and a failure reads as a failure.

Present since the feature shipped: the custom-instruction path has never
worked. Plain actions (refine, summarise, grammar, expand) were unaffected and
are now covered by tests so they stay that way.

docs/map/00-index.md

@@ -2,8 +2,8 @@
 
 > Status: ACTIVE
 > Last full audit: 2026-09-13
-> Last update: 2026-09-21 — CAP-16 (desktop key bindings rebuilt on one `@d3ro/core/keybinding` SSOT: multiple bindings per action, mouse buttons, `HOTKEY` → `KEYBINDING` IPC group); verified on Windows by a manual run, so CAP-16 and CAP-02 are `[x]` and GAP-KEY-01 is closed; GAP-KEY-02/03, GAP-QA-02, GAP-I18N-01/02, GAP-INFRA-06 remain open; `11` gained §7 for accepted design constraints (things deliberately kept, not gaps)
-> Scope: entire monorepo `D:/workspace/D3ROVoice` at product version `1.3.7`
+> Last update: 2026-09-21 — LLM instruction-prompt fix (`9c2b4d4`): the custom-instruction path inserted the instruction's own wording instead of the processed result and had **never worked in any shipped release** (`v0.1.0-alpha`..`v1.4.0`, introduced `fea923d` 2026-04-05, not a regression). `llm-prompts.ts` is now the SSOT for prompt resolution and placeholder substitution, shared by `VoiceModeService` / `ChainService` / `LLM.PROCESS`. AI-04/05/06/07 are demoted to `[~]` on desktop — fixed with unit tests, but **not verified in a running app** and the four related `tests/red/*.usecase.test.ts` could not execute (`better-sqlite3` ABI). New: GAP-LLM-01 (no target-language setting), GAP-LLM-02 (this fix unverified); GAP-INFRA-06 amended (the ABI masks verification, not just dev-env switching cost); GAP-I18N-01 amended (`popup.error.default` missing in 10 locales). Earlier the same day: CAP-16 (desktop key bindings rebuilt on one `@d3ro/core/keybinding` SSOT — multiple bindings per action, mouse buttons, `HOTKEY` → `KEYBINDING` IPC group), verified on Windows by a manual run, so CAP-16 and CAP-02 are `[x]` and GAP-KEY-01 is closed. Still open: GAP-KEY-02/03, GAP-QA-02, GAP-I18N-01/02, GAP-INFRA-06, GAP-LLM-01/02; `11` §7 holds accepted design constraints (things deliberately kept, not gaps)
+> Scope: entire monorepo `D:/workspace/D3ROVoice` at product version `1.4.0` (`release/product-version.json`, released 2026-09-21)
 > Purpose: let any agent (or human) answer two questions in under a minute:
 > 1. **What infrastructure exists?** (build, CI, services, APIs, data, packages, deploy)
 > 2. **How far is each feature developed?** (per surface, with file anchors and status)