Update docs to reflect 6 precheck steps (was 5)

This PR adds a 6th lint check (Fortran/Fypp analysis). Update
CLAUDE.md and common-pitfalls.md to match.

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

Author: sbryngelson

.claude/rules/common-pitfalls.md

@@ -54,7 +54,7 @@
 ## PR Checklist
 Before submitting a PR:
 - [ ] `./mfc.sh format -j 8` (auto-format)
-- [ ] `./mfc.sh precheck -j 8` (5 CI lint checks)
+- [ ] `./mfc.sh precheck -j 8` (6 CI lint checks)
 - [ ] `./mfc.sh build -j 8` (compiles)
 - [ ] `./mfc.sh test --only <relevant> -j 8` (tests pass)
 - [ ] If adding parameters: all 4 locations updated

CLAUDE.md

@@ -39,7 +39,7 @@ All commands run from the repo root via `./mfc.sh`.
 ./mfc.sh test --generate --only <feature>  # Regenerate golden files after intentional output change
 
 # Verification (pre-commit CI checks)
-./mfc.sh precheck -j 8                     # Run all 5 lint checks (same as CI gate)
+./mfc.sh precheck -j 8                     # Run all 6 lint checks (same as CI gate)
 ./mfc.sh format -j 8                       # Auto-format Fortran (.fpp/.f90) + Python
 ./mfc.sh lint                              # Pylint + Python unit tests
 ./mfc.sh spelling                          # Spell check
@@ -99,7 +99,7 @@ IMPORTANT: Follow this loop for ALL code changes. Do not skip steps.
 2. **Plan** — For multi-file changes, outline your approach before implementing.
 3. **Implement** — Make small, focused changes. One logical change per commit.
 4. **Format** — Run `./mfc.sh format -j 8` to auto-format.
-5. **Verify** — Run `./mfc.sh precheck -j 8` (same 5 checks as CI lint gate).
+5. **Verify** — Run `./mfc.sh precheck -j 8` (same 6 checks as CI lint gate).
 6. **Build** — Run `./mfc.sh build -j 8` to verify compilation.
 7. **Test** — Run relevant tests: `./mfc.sh test --only <feature> -j 8`.
    For changes to `src/common/`, test ALL three targets: `./mfc.sh test -j 8`.