Migrate internal architecture docs to docs/internal

docs/internal/prompts.md

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+# Audita Prompt Registry
+
+## Scope
+
+This document describes embedded prompt assets, prompt metadata, and rendering behavior.
+
+## Registry Ownership
+
+Prompt registry lives in `internal/prompts` and embeds assets under `internal/prompts/assets/**`.
+
+Registered prompt IDs:
+- `modules.glossary.proposal`
+- `modules.homophones.proposal`
+- `modules.spoken_word.proposal`
+- `modules.grammar.proposal`
+- `validators.spoken_form_plausibility`
+- `validators.meaning_reversal_review`
+- `validators.editorial_review`
+- `validators.grammar_review`
+- `validators.spoken_word_review`
+
+## Metadata Model
+
+Each prompt has metadata:
+- `prompt_id`
+- `prompt_version`
+- `prompt_source`
+- `embedded_path`
+- `sha256`
+
+Current source/version values:
+- `prompt_source = builtin`
+- `prompt_version = v1`
+
+## Rendering
+
+`prompts.RenderUserSystem(promptID, data)` renders system/user templates.
+
+Template behavior:
+- uses Go `text/template`;
+- `missingkey=error` is enabled;
+- output is trimmed.
+
+A shared hardening fragment is embedded once and referenced by prompt templates.
+
+## Prompt Context Inputs
+
+Shared prompt payload helpers:
+- transcript section JSON (`internal/framework/promptcontext/MarshalTranscriptSectionJSON`)
+- transcript description block (`TranscriptDescriptionBlock`)
+
+Modules and LLM validators provide typed data maps to render prompt assets.
+
+## Diagnostics Integration
+
+Prompt metadata is attached to proposal/validator diagnostics request metadata using `Metadata.DiagnosticsMap()`.
+
+## Key Tests
+
+- `internal/prompts/registry_test.go`
+- `internal/framework/promptcontext/*_test.go`
+- module and validator prompt builder tests