🤖 Fix proofreading issues in bevy skills

- Fix `ref` keyword used as variable name in code examples
- Fix "retries next tick" → systems continue on normal schedule
- Fix `State::set()` → `NextState::set()` in upgrade skill
- Fix `SceneRoot` → `WorldAssetRoot` for 0.19 consistency
- Fix Replace lifecycle event description (overwritten, not removed)
- Fix grep patterns (quoting, trailing spaces)
- Remove third-party physics/networking content (not Bevy built-ins)

plugins/bevy/skills/bevy-upgrade/SKILL.md

@@ -9,7 +9,7 @@ Bevy ships breaking changes every minor release. Upgrades are tractable if run a
 
 ## Workflow
 
-1. **Establish current and target versions.** Read `Cargo.toml` (`bevy` plus ecosystem crates: physics, UI, networking — each is pinned to a Bevy minor and must be bumped in lockstep).
+1. **Establish current and target versions.** Read `Cargo.toml` (`bevy` plus ecosystem crates — each is pinned to a Bevy minor and must be bumped in lockstep).
 2. **Upgrade one minor version at a time.** Skipping versions compounds renames and makes errors unattributable. For each bump:
    1. Bump `bevy` and every Bevy-ecosystem crate to versions compatible with the target. If an ecosystem crate has no compatible release, stop and surface it — that blocks the bump.
    2. `cargo check`, then apply the **rename table** for the transition (see references) across all errors. These are mechanical.
@@ -43,7 +43,7 @@ When `Cargo.toml` is ambiguous (workspace inheritance, git deps), the code itsel
 ## The traps of upgrading
 
 - **Renames that compile but misbehave**: some old names still exist with new meaning. `Event` compiles in 0.18+ but means observer-events, not buffered messages — a mechanical `EventWriter → MessageWriter` port is right, but a type left as `#[derive(Event)]` and "written" nowhere fires no observers silently.
-- **Behavior shifts need runtime verification**: `State::set()` same-state re-firing (0.18), transform-propagation reads, `Query<Entity>` matching resource entities (0.19). `cargo check` proves nothing here — run it.
+- **Behavior shifts need runtime verification**: `NextState::set()` same-state re-firing (0.18), transform-propagation reads, `Query<Entity>` matching resource entities (0.19). `cargo check` proves nothing here — run it.
 - **Ecosystem crates lag.** A Bevy bump is only as ready as its slowest dependency. Check compatibility before starting, not after.
 - **Don't modernize mid-bump.** During a bump, make the minimal change that satisfies the new API; idiomatic rewrites happen after the chain is complete (with the bevy-0.19 skill). Mixing the two makes regressions unattributable.