[All] Fix ~45 code scanning warnings in Fable.Transforms

[dbrattli]

Summary

• Address four categories of code scanning analyzer warnings across 15 files in src/Fable.Transforms/
• GRA-STRING-001/002/004: Add explicit StringComparison.Ordinal to StartsWith, EndsWith, and LastIndexOf string overloads
• IONIDE-007: Replace cons-nil list patterns (x :: []) with list literal patterns ([x]), also improving readability of complex multi-element patterns in Rust/Replacements.fs
• IONIDE-005: Replace s = "" conditionals with String.IsNullOrEmpty(s) for more efficient empty string testing
• GRA-TYPE-ANNOTATE-001: Add type annotations to ambiguous string function calls using string<type> syntax

Note: GRA-INTERPOLATED-001 (:s/:d format specifiers) was attempted but reverted — the Standalone tests compile the compiler to JavaScript via Fable, which doesn't handle .NET-style format specifiers correctly.

Test plan

• dotnet build src/Fable.Transforms/Fable.Transforms.fsproj — 0 errors, 0 warnings
• ./build.sh test javascript --skip-fable-library — 2,603/2,607 passed (4 failures are pre-existing locale-dependent Convert format tests)
• CI pipeline passes

🤖 Generated with Claude Code

[github-advanced-security]

Ionide.Analyzers.Cli found more than 20 potential problems in the proposed changes. Check the Files changed tab for more details.

[github-actions]

Python Type Checking Results (Pyright)

Metric	Value
Total errors	18
Files with errors	4
Excluded files	4
New errors	✅ No

Excluded files with errors (4 files)

These files have known type errors and are excluded from CI. Remove from pyrightconfig.ci.json as errors are fixed.

File	Errors	Status
temp/tests/Python/test_applicative.py	12	Excluded
temp/tests/Python/test_hash_set.py	3	Excluded
temp/tests/Python/test_nested_and_recursive_pattern.py	2	Excluded
temp/tests/Python/fable_modules/thoth_json_python/encode.py	1	Excluded