v0.18.3 — green CI bundle

Patch release on top of v0.18.2.

Why this exists

v0.18.2 was tagged correctly but the tagged tree carried two pre-existing CI blockers that the prior releases never caught (CI had been red on the last five commits for unrelated reasons). Verifying the new template-pin guard fires on the runner surfaced them. v0.18.3 cuts a tag that ships with all 15 CI steps green.

Fixed

• cargo fmt --check clean on the whole workspace. Pre-existing rustfmt drift in crates/rio-theme/ (introduced with the crate in 0.17.0 and never run through fmt locally) plus the CLI's theme.rs. Mechanical reformat, no behavior change.

• clippy::uninlined-format-args violation in crates/rio-theme/src/color.rs. CI pins rustc 1.88, whose clippy enforces this as a hard error under -D warnings; newer local toolchains are lenient.

  -format!(\"#{:02x}{:02x}{:02x}\", r, g, b)
  +format!(\"#{r:02x}{g:02x}{b:02x}\")

  Same lint class that bit bcdf9b6 last quarter — flagging for the release checklist.

Verified

• All 15 CI steps green on run 26337327486 (the v0.18.3 release commit itself): fmt, clippy, build, test, Tier-2 symbol guard, four Builder Doctrine guards, and the new scaffold-template-pin guard.
• The template-pin guard's FAIL path independently verified on run 26337205216 via throwaway PR #2 (closed without merge): every other step green, only the guard step failed with the expected actionable error message:

  ::error::Workspace version (0.18.2) and scaffold template pin (0.16.0) have drifted.
  Update crates/rustio-admin-cli/templates/project/Cargo.toml.tmpl to read
  'rustio-admin = \"0.18.2\"'. See v0.18.1 release notes for the convention.
  

Compatibility

• No library API change.
• No CLI surface change.
• Drop-in upgrade from 0.18.2.
• Release checklist note: run cargo +1.88 clippy and cargo fmt --check locally before tagging. CI catches it but earlier feedback is cheaper.