Add optional narrowing and payload access

[itsfuad]

Summary

• add module-owned FlowTyped results between CFG and definite initialization
• narrow stable optional variables, fields, nested projections, constant indexes, and resolved binding indexes across full CFG fixed points
• preserve carrier types in explicit optional contexts while exposing inferred payload types at proven uses
• invalidate facts through assignments, aliases, index dependencies, calls, raw pointers, globals, and scope exit
• make ownership consume flow payload/origin evidence and lower presence/payload operations explicitly through HIR, MIR, and LLVM
• publish refined hover types and flow diagnostics through incremental LSP snapshots

Ownership boundary

• copyable and shared-reference payload reads preserve optional carrier
• moving move-only payload from direct named local or parameter consumes whole carrier and supports reinitialization
• move-only extraction from fields, indexes, pointees, and other partial places remains rejected

Representation boundary

• every optional remains tagged {present, value} in this PR
• niche representation remains separate in Add optional niche layouts #30
• no Some, unwrap, fallback, chaining, patterns, optional equality, or other new syntax

Validation

• CCACHE_DISABLE=1 GOCACHE=/tmp/peeper-go-cache go test -count=1 ./...
• CCACHE_DISABLE=1 GOCACHE=/tmp/peeper-go-cache go vet ./...
• CCACHE_DISABLE=1 GOCACHE=/tmp/peeper-go-cache go test -race -count=1 ./...
• CCACHE_DISABLE=1 GOCACHE=/tmp/peeper-go-cache bash scripts/build.sh
• CCACHE_DISABLE=1 GOCACHE=/tmp/peeper-go-cache PEEPER_BIN="$PWD/build/bin/peeper" go test -count=1 ./x_test
• git diff --check

Closes #28.

Follow-up: #31 can use delivered optional payload contract for iterator next -> ?T; #30 remains open for niche layouts.