chore: DX improvements — typos, blame-ignore, PR template, registry checklist (#120)

* chore: add workspace clippy lints, release profiles, COMPAT.md, diff-registry.sh

- Workspace clippy lints: or_fun_call, redundant_clone, collection_is_never_read,
  naive_bytecount, stable_sort_primitive, large_types_passed_by_value, assigning_clones
- Fix or_fun_call in cargo_registry.rs (unwrap_or -> unwrap_or_else)
- Release profiles: release (thin LTO) + release-official (full LTO, codegen-units=1)
- COMPAT.md: protocol compatibility matrix for all 7 registries (40 endpoints)
- scripts/diff-registry.sh: differential smoke tests (Docker/npm/Cargo/PyPI/Go/Raw)

* ci: add typos spell-check job and config

* chore: add .git-blame-ignore-revs for bulk fmt/clippy commits

* chore: unify PR template with What/Why/Checklist format

* docs: add new registry checklist and improve contributing guide

* fix: correct typos action SHA to v1.45.0

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,16 +1,14 @@
-## Summary
+## What
 
-<!-- What does this PR do? -->
+<!-- Brief description of changes -->
 
-## Changes
+## Why
 
-<!-- List key changes -->
+<!-- Motivation / issue reference -->
 
 ## Checklist
 
-- [ ]  passes
-- [ ]  passes
-- [ ]  passes
-- [ ] No  in production code
-- [ ] New public API has documentation
-- [ ] CHANGELOG updated (if user-facing change)
+- [ ] Tests pass (`cargo test`)
+- [ ] No new clippy warnings (`cargo clippy -- -D warnings`)
+- [ ] Updated CHANGELOG.md (if user-facing change)
+- [ ] New registry? See CONTRIBUTING.md checklist