refactor(config): split ParseConfig into tokenise, dispatch, clamp and sanitize helpers

docs/architecture/08-config-profiles.md

@@ -73,6 +73,11 @@ as an initializer, so a missing or malformed key keeps the default; parsing neve
 - `model` must be `render`, `transform` or `hybrid`; anything else becomes `hybrid`.
 - Unsafe binds read as unbound (`src/keybind_rules.h`, [06](06-input.md)).
 - `LoadConfig` is the I/O wrapper, excluded from the test build by `WIND_TESTS`.
+- Structure: per line `SplitIniLine` (key and value), `ApplyEmptyableKey` (the exe lists and
+  `engine*`, which accept an empty value), then `ApplyValueKey` (one parser per key; a bad value
+  throws and keeps the default). After the loop `ClampConfig` (ranges, the `renderScaling`
+  migration, the `model` fallback) and `SanitizeBinds`. A new key goes in `ApplyValueKey`, its
+  range in `ClampConfig`.
 
 ## Hot-reload and the UI-only fingerprint
 

docs/architecture/09-settings-ui.md

@@ -106,7 +106,7 @@ and default. `Settings.svelte` is the shell (title bar, sidebar, banner, save ca
 - **Removed from the UI is not removed from the product.** Many keys have no row (quick zoom
   setup, outline, `sharpness`, `multiMonitor`, the `tx*` knobs). The core still parses
   them, and Open settings file is the way to edit them.
-- Adding a setting is normally a schema row plus a `ParseConfig` entry.
+- Adding a setting is normally a schema row plus a `ParseConfig` entry (`ApplyValueKey`, see 08).
 - Copy rules (in the schema header): plain language, no toggle label starting with "Enable", no
   description that restates its label.