doc: silence rustdoc intra-doc warnings (private-item links and palette/surface ambiguities)

`cargo doc --no-deps` was emitting eight warnings about intra-doc links resolving to private items or ambiguous fn/module names. None reflect a behaviour bug; they were just noise that cluttered the docs build output.
Five of the warnings came from doc comments that cross-referenced items not in the rendered public API. `widget::scroll::Scroll` (struct), `Scroll::horizontal`, `Scroll::both`, `event_loop::text_editing` (module) and `text_shaping` (module) are all `pub` in their own modules, but the `widget` and `event_loop` parents are private to the crate root, so rustdoc treats them as private when resolving links from items that ARE on the public surface (`ScrollAxis`, the `scroll` constructor, `font_bytes`, the `text_edit` module docs). The fix is to drop the link syntax for those references: keep the identifier in backticks (so it still renders as code) but remove the surrounding `[...]` so rustdoc doesn't try to resolve it. Where the cross-reference had no semantic load beyond "see this module", the prose is rephrased to name the module without trying to link to it (e.g. "the `event_loop::text_editing` private module", "see the `text_shaping` private module").
The remaining three warnings were `palette` / `surface` linking ambiguously between a module of that name and a function of the same name within `crate::theme`. Adding `()` after the identifier inside the brackets (`palette` → `palette()`, `surface` → `surface()`) disambiguates to the function, which is the intent in all three sites — the surrounding text talks about "per-slot shorthand accessors", which is what the functions are.
After this `cargo doc --no-deps` runs clean with no warnings.

src/gles_render/mod.rs

@@ -138,7 +138,7 @@ pub struct GlesCanvas
 	/// theme registry.
 	pub font:         Arc<Font>,
 	/// Raw bytes of the default font. Required by rustybuzz for
-	/// HarfBuzz shaping (see [`crate::text_shaping`]). Kept on the
+	/// HarfBuzz shaping (see the `text_shaping` private module). Kept on the
 	/// canvas so the shape pipeline has direct access without a
 	/// global lookup.
 	pub font_bytes:   Arc<Vec<u8>>,