fix: record type aliases now work for unification and field access

Expand type aliases via unify_with_env() everywhere in the type checker,
not just in a few places. This fixes named record types like
`type Vec2 = { x: Float, y: Float }` — they now properly unify with
anonymous records and support field access (v.x, v.y).

Also adds scripts/validate.sh for automated full-suite regression
testing (Rust tests + all 5 package test suites + type checking).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -42,15 +42,34 @@ When making changes:
 7. **Fix language limitations**: If you encounter parser/type system limitations, fix them (without regressions on guarantees or speed)
 8. **Git commits**: Always use `--no-gpg-sign` flag
 
-### Post-work checklist (run after each major piece of work)
+### Post-work checklist (run after each committable change)
+
+**MANDATORY: Run the full validation script after every committable change:**
+```bash
+./scripts/validate.sh
+```
+
+This script runs ALL of the following checks and will fail if any regress:
+1. `cargo check` — no Rust compilation errors
+2. `cargo test` — all Rust tests pass (currently 387)
+3. `cargo build --release` — release binary builds
+4. `lux test` on every package (path, frontmatter, xml, rss, markdown) — all 286 package tests pass
+5. `lux check` on every package — type checking + lint passes
+
+If `validate.sh` is not available or you need to run manually:
 ```bash
 nix develop --command cargo check       # No Rust errors
-nix develop --command cargo test        # All tests pass (currently 381)
-./target/release/lux check              # Type check + lint all .lux files
-./target/release/lux fmt                # Format all .lux files
-./target/release/lux lint               # Standalone lint pass
+nix develop --command cargo test        # All Rust tests pass
+nix develop --command cargo build --release  # Build release binary
+cd ../packages/path && ../../lang/target/release/lux test        # Package tests
+cd ../packages/frontmatter && ../../lang/target/release/lux test
+cd ../packages/xml && ../../lang/target/release/lux test
+cd ../packages/rss && ../../lang/target/release/lux test
+cd ../packages/markdown && ../../lang/target/release/lux test
 ```
 
+**Do NOT commit if any check fails.** Fix the issue first.
+
 ### Commit after every piece of work
 **After completing each logical unit of work, commit immediately.** Do not let changes accumulate uncommitted across multiple features. Each commit should be a single logical change (one feature, one bugfix, etc.). Use `--no-gpg-sign` flag for all commits.
 
@@ -109,7 +128,7 @@ When working on any major task that involves writing Lux code, **document every
 ## Code Quality
 
 - Fix all compiler warnings before committing
-- Ensure all tests pass (currently 381 tests)
+- Ensure all tests pass (currently 387 tests)
 - Add new tests when adding features
 - Keep examples and documentation in sync