Add weighted path sidecar

[MesTTo]

Adds a derived weighted-path sidecar over encoded MORK paths.

The branch keeps signed path weights outside the authoritative PathMap<()> atom store, supports set and delta updates, tracks positive-weight totals, and selects paths by cumulative positive-weight offset. Negative weights are retained as maintenance state but are ignored by weighted selection.

Validation:

• cargo +nightly-2026-06-01 test -p mork --test weighted_paths with RUSTFLAGS='-C target-cpu=native'
• CARGO_HOME=/home/user/Dev/.cargo-isolated RUSTFLAGS='-C target-cpu=native -Awarnings' cargo +nightly test -p mork --test public_api
• cargo +nightly-2026-06-01 test -p mork --lib with RUSTFLAGS='-C target-cpu=native'
• rustfmt --check on kernel/src/weighted_paths.rs, kernel/tests/weighted_paths.rs, and kernel/tests/public_api.rs
• jscpd on kernel/src/weighted_paths.rs, kernel/tests/weighted_paths.rs, and kernel/tests/public_api.rs
• git diff --check

[MesTTo]

Folding this into #101: its two commits are the strict prefix of that branch, which adds the Catamorphism-built selection tree and wires the primitive as the (wselect ...) grounded sink behind a default-off feature, with tests and a runnable resource. #101 is mergeable against current main; this branch conflicts. One wired PR to review instead of an un-wired base.