docs: add agent guidance and historical audit report

Add root AGENT.md with project conventions, build verification steps,
source layout, style rules, and real-time/concurrency requirements.
Add per-module AGENT.md files for each existing and proposed source
subdirectory. Add AUDIT_REPORT.md as a historical Phase 1 snapshot
documenting memory management, error handling, concurrency model,
naming conventions, and anti-pattern catalog.

Source/Resources/AGENT.md

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+# resources module
+
+## Owned files
+
+- Related embedded assets and helpers: `../Resources.h`, `../Resources.cpp`
+- logo.svg
+- background.svg
+
+## Rules
+
+- Keep every theme colour in `namespace theme` in Resources.h.
+- Embed SVG assets as raw string literals.
+- Keep formatting helpers (formatPercent, formatHz, formatSeconds, formatSemis, formatCents, formatPan, formatInt) here.
+- Use `maps::` from Params for unit conversions in formatters.
+- Never hardcode a theme colour in a widget; reference `theme::`.
+
+## IF-THEN
+
+- IF a widget needs a colour THEN reference a `theme::` entry rather than a literal Colour.
+- IF an SVG asset ships under Source/Resources THEN keep its embedded string in Resources.cpp consistent with the file.
+
+## Examples
+
+```cpp
+// BAD: hardcoded colour in a widget
+g.setColour (juce::Colour (0xff4fc3f7));
+```
+
+```cpp
+// GOOD: theme is the single source
+g.setColour (theme::accent);
+```
+
+This file overrides /AGENT.md where they conflict.