fix: Re-enable lagrange_generator.jl include for existing basis files

**Problem:** CI documentation build failing with:
  UndefVarError: `create_basis_and_eval` not defined

**Root Cause:**
- Commented out include("basis/lagrange_generator.jl")
- But existing lagrange_*.jl files still use create_basis_and_eval()
- Generator must be loaded at runtime (for now)

**Solution:**
- Re-enable include("basis/lagrange_generator.jl")
- Add TODO comment explaining this is temporary
- Once we generate lagrange_generated.jl, we can:
  1. Remove old lagrange_*.jl includes
  2. Include lagrange_generated.jl instead
  3. Remove lagrange_generator.jl from runtime

**Status:**
- ✓ Package loads successfully
- ✓ Should fix CI documentation build

**Next Steps:**
1. Run scripts/generate_lagrange_basis.jl
2. Create src/basis/lagrange_generated.jl
3. Replace dynamic includes with static generated file
4. Remove __precompile__(false) completely

src/JuliaFEM.jl

@@ -137,9 +137,9 @@ end
 include("basis/abstract.jl")
 include("basis/subs.jl")  # Symbolic substitution (includes minimal simplify from SymDiff.jl)
 include("basis/vandermonde.jl")
-# NOTE: lagrange_generator.jl is NOT included here - it's a tool, not runtime code!
-# It's only loaded by scripts/generate_lagrange_basis.jl during pre-generation.
-# The generated code is in lagrange_generated.jl (to be created).
+# TODO: Replace dynamic basis generation with pre-generated file
+# For now, still need this for existing lagrange_*.jl files
+include("basis/lagrange_generator.jl")
 include("basis/lagrange_segments.jl")
 include("basis/lagrange_quadrangles.jl")
 include("basis/lagrange_triangles.jl")