Refresh docs/options.md to track remaining bindgen option cleanup

[Copilot]

• Audit current windows-bindgen CLI/builder options against docs/options.md
• Confirm "Already landed" items match code
• Confirm no listed options are now nonexistent
• Refresh docs/options.md (first pass)
• Implement §3 proposed option set:
  • Add public DepMode { Core, Specific, None } enum
  • Replace Bindgen::no_deps()/specific_deps() with Bindgen::deps(DepMode)
  • Replace Bindgen::sys_fn_extern() with Bindgen::extern_fns()
  • CLI: replace --no-deps/--specific-deps with --deps <core|specific|none> and --sys-fn-extern with --extern
  • Parse-time validation: reject --no-toml without --package and --extern without --sys
• Update internal callers (fixtures.rs, fixture .tomls, samples, tests, crates/tools/bindings/*.txt)
• Regenerate bindings via cargo run -p tool_bindings --release (no diff)
• Run cargo fmt --all, cargo clippy -p windows-bindgen --all-targets, cargo test -p test_bindgen --test fixtures, cargo check --all-targets
• Remove §3 (and obsolete §4/§5/§6 plan sections) from docs/options.md; fold migration table into "Already landed"